Why is Covid-19 more contagious than SARS or MERS?

From the beginning of the Covid-19 pandemic, it was evident that SARS-CoV2, the agent of Covid-19, was more contagious than other well-known coronaviruses that cause SARS or MERS. Based on a fascinating “shell disorder model, the reason may lie in the “odd” combination of “hardiness” of its membrane protein (M) (outer shell) making it more likely to survive in body fluids and environment, and resilience of its nuclear protein (N) (inner shell) making it more likely to rapidly replicate even before the immune system detects it.1

Outer shell hardiness of the M protein of SARS-CoV2 contributes to its persistence in the environment and resistance to digestive enzymes in saliva, mucus, stool, and other bodily fluids. Inner shell resilience of the N protein can lead to greater virulence through more rapid replication of viral proteins and particles. The latter is also an efficient way of evading the host immune system ie, by the time the immune system finds out there is a problem, the virus has already reproduced in high numbers in the absence of symptoms!

Long before Covid-19 pandemic, a group of scientists proposed categorization of coronaviruses into 3 major “shell disorder” categories (based on the features of the M and N proteins), correlating with their primary modes of transmission. Category A: higher levels of respiratory transmission, lower levels of fecal-oral transmission (eg. HCoV-229E, common cold coronavirus); category B: intermediate levels of respiratory and fecal-oral transmission (eg, SARS-CoV); and category C: lower levels of respiratory transmission with higher levels of fecal-oral transmission (eg, MERS).1,2  

It turns out that Covid-19 falls into category B which means that it has the potential for transmission not only through respiratory route but also through fecal-oral route and the environment. What’s “odd” about SARS-CoV2 though is that it seems to have the hardiest outer shell compared to SARS-CoV and other coronaviruses in its category.

So not only is Covid-19 more likely to be transmitted due to high viral loads in the respiratory tract even before symptoms develop, it may have an advantage over other respiratory coronaviruses by persisting in the environment when contaminated by respiratory secretions, feces or other body fluids.

Truly a “novel” virus!

Bonus Pearl: Did you know that despite being more contagious, Covid-19 is fortunately less fatal than SARS or MERS?

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References

  1. Goh GKM, Dunker AK, Foster JA, Uversy VN. Shell disorder analysis predicts greater resilience of the SARS-CoV-2 (COVID-19) outside the body and in body fluids. Microbial pathogenesis 2020;144:104177. https://pubmed.ncbi.nlm.nih.gov/32244041/
  2. Goh GKM, Dunker AK, Uversky VN. Understanding viral transmission behavior via protein intrinsic disorder prediction: Coronaviruses. J Pathol 2012;2012:738590. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3477565/

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Why is Covid-19 more contagious than SARS or MERS?

My 75 year old patient has an arterial oxygen tension (Pa02) less than 90 mmHg on room air. Does age affect PaO2?

Short answer: Yes! Most studies of blood gas concentrations have demonstrated a decrease in oxygen tension with age.1

Earlier studies have demonstrated a linear decrease in oxygen tension based on observations that included relatively small number of patients over the age of 60. 1 More recently, however, in a study of 532 consecutive patients admitted for elective surgery without overt cardiac, pulmonary, or metabolic disease, obesity or smoking, the mean PaO2 differed by age group as follows:

  • <30 years: 98.4 mmHg
  • 30-50 years: 88.7 mmHg
  • 51-70 years: 81.0 mmHg
  • >70 years: 76.5 mmHg

After age 70 years, decline in Pa02 may slow down or actually reverse, likely related to the “survival of the fittest” in more advanced years. 1,2 Some have suggested accepting a PaO2 80-85 mmHg as normal for subjects > 65 years of age. 3

The decrease in PaO2 with age is a result of increased heterogeneity of ventilation/perfusion ratio, especially reduced ventilation in the dependent parts of the lung. 3 Aging is also associated with a decrease in chest wall compliance, muscle (including the diaphragm) strength, forced expiratory volume in 1 second (FEV1), vital capacity, and diffusing capacity of carbon monoxide (DLC0)/alveolar volume.  

In addition, aging is associated with a reduction in response to hypoxia and hypercarbia, making older patients particularly vulnerable to complications from  heart failure and pneumonia4, especially in the current Covid-19 era.

Bonus Pearl: Did you know that poor response to hypoxic or hypercarbic states in the elderly is likely related to an age-related decline in efferent neural output to respiratory muscles?4

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References

  1. Blom H, Mulder M, Verwej W. Arterial oxygen tension and saturation in hospital patients: effect of age and activity. BMJ 1988;297:720-2. Doi:10.1136/bmj.297.6650.720 https://www.bmj.com/content/297/6650/720   
  2. Delclaux B, Orcel B, Housset B, et al. Arterial blood gases in elderly persons with chronic obstructive pulmonary disease (COPD). Eur Respir J 1994;7:856-61. https://www.researchgate.net/publication/15147788_Arterial_blood_gases_in_elderly_persons_with_chronic_obstructive_pulmonary_disease_COPD
  3. Janssens JP, Pache JC, Nicod LP. Physiological changes in respiratory function associated with ageing. Eur Respir J 1999;13:197-205. https://www.researchgate.net/publication/12689073_Physiological_changes_in_respiratory_function_associated_with_ageing
  4. Sharma G, Goodwin J. Effect of aging on respiratory system physiology and immunology. Clin Interventions in Aging 2006;1:253-60. https://pubmed.ncbi.nlm.nih.gov/18046878/

 

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

 

 

My 75 year old patient has an arterial oxygen tension (Pa02) less than 90 mmHg on room air. Does age affect PaO2?

What is the role of prone ventilation in patients with Covid-19 and ARDS?

A 2017 guideline strongly recommends the use of prone ventilation for 12+ hours daily in individuals with severe ARDS (1). A JAMA article gave similar recommendations for critically ill patients with COVID-19 (2).

The recommendations are often based on a NEJM 2013 randomized-controlled study involving 466 patients with severe ARDS (3). While previous research had demonstrated improved oxygenation in the prone position (4), this study demonstrated a significant survival benefit (3).  Mortality at 28 days was 16.0% in prone patients versus 32.8% in supine patients (p<0.001; HR 0.39 with 95% CI, 0.29 – 0.67) (3). Mortality was also lower in prone patients at 90 days (3).  A meta-analysis of 4 additional randomized-controlled trials confirmed the survival benefits (1). 

In patients with Covid-19 and ARDS, a small retrospective study involving 12 patients showed a significant association between prone positioning and lung recruitability (ie, lung tissue in which aeration can be restored) (p = 0.020) (5).

Physiologically, numerous mechanisms have been proposed for these findings, including the possbility that while blood flow consistently favors the dorsal alveoli regardless of position, the prone position allows dorsal alveoli to reopen, improving ventilation/perfusion matching (6). 

Of note, some institutions find difficulties with prone positioning, including higher rates of pressure sores and endotracheal tube obstruction (1).

 

Contributed by Grant Steele, Harvard Medical Student, Boston, MA.

 

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References:

1. Fan E, Del Sorbo L, Goligher E, et al. An official American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine clinical practice guideline: mechanical ventilation in adult patients with acute respiratory distress syndrome.” Am J Respir Crit Care Med 2017;195:1253-1263. https://www.atsjournals.org/doi/abs/10.1164/rccm.201703-0548ST 
2. Murthy S, Gomersall C, & Fowler R. Care for critically ill patients with COVID-19. JAMA – Published online March 11, 2020. doi:10.1001/jama.2020.3633 https://jamanetwork.com/journals/jama/fullarticle/2762996
3. Guérin C, Reignier J, Richard J-C, et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med 2013;368:2159-2168. https://www.nejm.org/doi/full/10.1056/nejmoa1214103
4. Abroug F, Ouanes-Besbes L, Elatrous S, et al. The effect of prone positioning in acute respiratory distress syndrome or acute lung injury: a meta-analysis. Areas of uncertainty and recommendations for research. Intensive Care Medicine – Published online March 19, 2008. doi: 10.1007/s00134-008-1062-3 https://link.springer.com/article/10.1007/s00134-008-1062-3
5. Pan C, Chen L, Lu C, et al. Lung Recruitability in SARS-CoV-2 Associated Acute Respiratory Distress Syndrome: A Single-center, Observational Study. Am J Respir Crit Care Med – Published online March 23, 2020. doi: 10.1164/rccm.202003-0527LE. https://www.atsjournals.org/doi/pdf/10.1164/rccm.202003-0527LE 
6. Nyrén S, Mure M, Jacobsson H, et al. Pulmonary perfusion is more uniform in the prone than in the supine position: scintigraphy in healthy humans. J Appl Physiol 1999;86:1135-1141. https://www.physiology.org/doi/abs/10.1152/jappl.1999.86.4.1135

 

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

What is the role of prone ventilation in patients with Covid-19 and ARDS?

Should I continue or discontinue angiotensin converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) in my patients with possible Coronavirus/Covid-19 infection?

The original reports of an association between hypertension and increased risk of mortality in hospitalized patients with Covid-19 infection raised concern over the potential deleterious role of ACEIs or ARBs in such patients.1-4 However, as stated by a joint statement of several cardiology societies, including the American Heart Association, American College of Cardiology and the European Society of Cardiology on March 13, 2020, there is no clinical or scientific evidence that ACEI or ARBS should be routinely discontinued in patients with Covid-19 infection.5

In fact, some have argued for the opposite ie, consideration for the use of ARBs, such as losartan (an angiotensin receptor 1 [AT1R] antagonist), in patients with Covid-19.6,7  Although it is true that Covid-19 appears to use ACE2 as a binding site to infect cells (just as in SARS) and that ACE2 may be upregulated in patients on chronic ACEI or ARBs,8,9 ACE2 may also potentially protect against severe lung injury associated with infections.10,11  

Two complementary mechanisms have been posited for the potential protective effect of ARBs in Covid-19 infection-related lung injury: 1. Blocking the excessive AT1R activation caused by the viral infection; and 2. Upregulation of ACE2, thereby reducing production of angiotensin II and increasing the production of the vasodilator angiotensin 1-7.7

In the absence of proper clinical studies, it is premature, however, to recommend use of losartan or other AT1R antagonists as a means of reducing the likelihood of ARDS in patients with Covid-19 at this time.

Bonus Pearl: Did you know that ARDS is a major cause of death in Covid-19 infection?12

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References

  1. Guan W, Ni Z, Hu Y, et al. Clinical characteristics of coronavirus disease 2019 in China. N Engl J Med 2020, March 6. https://www.nejm.org/doi/pdf/10.1056/NEJMoa2002032?articleTools=true
  2. O’Mara GJ. Could ACE inhibitors, and particularly ARBs, increase susceptibility to COVID-19 infection? BMJ 2020;368:m406 ARTICLE
  3. Sommerstein R, Grani C. Preventing a Covid-19 pandemic: ACE inhibitors as a potential risk factor for fatal Covid-19. BMJ2020;368:m810. https://www.bmj.com/content/368/bmj.m810/rr-2
  4. Li X, Geng M, Peng Y, et al. Molecular immune pathogenesis and diagnosis of COVID-19. Journal of Pharmaceutical Analysis 2020, doi htps://doi.org/10.106/j.jpha.2020.03.001. https://www.sciencedirect.com/science/article/pii/S2095177920302045
  5. Cardiology societies recommend patients taking ACE inhibitors, ARBs who contract COVID-19 should continue treatment. March 17, 2020. https://www.healio.com/cardiology/vascular-medicine/news/online/%7Bfe7f0842-aecb-417b-9ecf-3fe7e0ddd991%7D/cardiology-societies-recommend-patients-taking-ace-inhibitors-arbs-who-contract-covid-19-should-continue-treatment
  6. Gurwitz D. Angiotensin receptor blockers as tentative SARS-CoV-2 therapeutics. Drug Dev Res 2020;1-4. https://www.ncbi.nlm.nih.gov/pubmed/32129518/
  7. Phadke M, Saunik S. Response to the emerging novel coronavirus outbreak. BMJ 2020;368:m406. https://www.bmj.com/content/368/bmj.m406/rr-2
  8. Zheng YY, Ma YT, Zhang JY, et al. COVID-19 and the cardiovascular system. Nature Reviews/Cardiology 2020; https://doi.org/10.1038/s41569-020-0360-5 .
  9. Ferrario CM, Jessup J, Chappell MC, et al. Effect of angiotensin-converting enzyme inhibition and angiotensin II receptor blockers on cardiac angiotensin-converting enzyme 2. Circulation 2005;111:2605-2610. https://www.ahajournals.org/doi/full/10.1161/circulationaha.104.510461
  10. Kuba K, Imai Y, Rao S, et al. A crucial role of angiotensin converting enzyme 2 (ACE2) in SARS coronavirus-induced lung injury. Nature Medicine 2005;11:875-79. Doi:10.1038/nm1267 https://www.nature.com/articles/nm1267?v=1
  11. Tikellis C, Thomas MC. Angiotensin-converting enzyme 2 (ACE2) is a key modulator of the renin angiotensin system in health and disease. International Journal of Peptides. Volume 2012, Article ID 256294, 8 pages. Doi:10.1155/2012/256294. https://research.monash.edu/en/publications/angiotensin-converting-enzyme-2-ace2-is-a-key-modulator-of-the-re

12 . Huang C, Wang Y, Li X, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 2020. https://doi.org/10.1016/S0140-6736(20)30183-5

 

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Should I continue or discontinue angiotensin converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) in my patients with possible Coronavirus/Covid-19 infection?

When should I consider a switch to oral antibiotics and discharge from hospital in my recently admitted elderly patient with community-acquired pneumonia (CAP)?

A frequently used validated set of clinical stability criteria in patients with CAP and supported by the 2019 ATS/IDSA CAP guidelines consists of a temperature ≤37.8 ᵒC (100.0 ᵒF) AND no more than 1 CAP-related sign of clinical instability as listed below: 1-3

  • Heart rate >100/min
  • Systolic blood pressure <90 mm Hg
  • Respiration rate >24 breaths/min
  • Arterial oxygen saturation <90% or Pa02<60 mm Hg (room air)

Using these criteria, the risk of clinical deterioration serious enough to necessitate transfer to an intensive care unit may be 1% or less, 1 while failure to achieve clinical stability within 5 days is associated with higher mortality and worse clinical outcome. 2 The median time to clinical stability (as defined) for CAP treatment is 3 days.1  

A 2016 randomized-controlled trial involving patients hospitalized with CAP found that implementation of above clinical stability criteria was associated with safe discontinuation of antibiotics after a minimum of 5 days of appropriate therapy.

Potential limitations of the above study include heavy use of quinolones (80%), underrepresentation of patients with severe CAP (Pneumonia Risk Index, PSI, V), and exclusion of nursing home residents, immunosuppressed patients, those with chest tube, or infection caused by less common organisms, such as Staphylococcus aureus or Pseudomonas aeruginosa.

Lack of clinical stability after 5 days of CAP treatment should prompt evaluation for complications of pneumonia (eg, empyema, lung abscess), infection due to  organisms resistant to selected antibiotics, or an alternative source of infection/inflammatory/poor response. 2

References

  1. Halm, EA, Fine MJ, Marrie TJ, et al. Time to clinical stability in patients hospitalized with community-acquired pneumonia: implications for practice guidelines. JAMA 1998;279:279:1452-57. https://reference.medscape.com/medline/abstract/9600479
  2. Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia. Am J Respir Crit Care Med 2019;200:e45-e67. https://www.ncbi.nlm.nih.gov/pubmed/31573350
  3. Uranga A, Espana PP, Bilbao A, et al. Duration of antibiotic treatment in community-acquired pneumonia. A multicenter randomized clinical trial. JAMA Intern Med 2016;176:1257-65. https://www.ncbi.nlm.nih.gov/pubmed/27455166/
When should I consider a switch to oral antibiotics and discharge from hospital in my recently admitted elderly patient with community-acquired pneumonia (CAP)?

What changes should I consider in my treatment of hospitalized patients with community-acquired pneumonia (CAP) in light of the 2019 guidelines of the American Thoracic society (ATS) and Infectious Diseases Society of America (IDSA)?

Compared to 2007,1 the 2019 ATS/IDSA guidelines2 propose changes in at least 4 major areas of CAP treatment in inpatients, with 2 “Do’s” and 2 “Dont’s”:

  • Do select empiric antibiotics based on severity of CAP and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (see related pearl on P4P)
  • Do routinely treat CAP patients who test positive for influenza with standard CAP antibiotics
  • Don’t routinely provide anaerobic coverage in aspiration pneumonia (limit it to empyema and lung abscess) (see related pearl on P4P)
  • Don’t routinely treat CAP with adjunctive corticosteroids in the absence of refractory shock

β-lactam plus macrolide is recommended for both non-severe and severe CAP.  β-lactam plus respiratory fluoroquinolone is an alternative regime in severe CAP, though not endorsed as strongly as β-lactam plus macrolide therapy (low quality of evidence).  Management per CAP severity summarized below:

  • Non-severe CAP
    • β-lactam (eg, ceftriaxone, cefotaxime, ampicillin-sulbactam and newly-added ceftaroline) plus macrolide (eg, azithromycin, clarithromycin) OR respiratory fluoroquinolone (eg, levofloxacin, moxifloxacin)
    • In patients at risk of MRSA or P. aeruginosa infection (eg, prior isolation of respective pathogens, hospitalization and parenteral antibiotics in the last 90 days or locally validated risk factors—HCAP has been retired), obtain cultures/PCR
    • Hold off on MRSA or P. aeruginosa coverage unless culture/PCR results return positive.
  • Severe CAP
    • β-lactam plus macrolide OR β-lactam plus respiratory fluoroquinolone (see above)
    • In patients at risk of MRSA or P. aeruginosa infection (see above), obtain cultures/PCR
    • Add MRSA coverage (eg, vancomycin or linezolid) and/or P. aeruginosa coverage (eg, cefepime, ceftazidime, piperacillin-tazobactam, meropenem, imipenem) if deemed at risk (see above) while waiting for culture/PCR results

Duration of antibiotics is for a minimum of 5 days for commonly-targeted pathogens and a minimum of 7 days for MRSA or P. aeruginosa infections, irrespective of severity or rapidity in achieving clinical stability.

For patients who test positive for influenza and have CAP, standard antibacterial regimen should be routinely added to antiinfluenza treatment.

For patients suspected of aspiration pneumonia, anaerobic coverage (eg, clindamycin, ampicillin-sulbactam, piperacillin-tazobactam) is NOT routinely recommended in the absence of lung abscess or empyema.

Corticosteroids are NOT routinely recommended for non-severe (high quality of evidence) or severe (moderate quality of evidence) CAP in the absence of refractory septic shock.

Related pearls on P4P:

2019 CAP guidelines on diagnostics:                                        https://pearls4peers.com/2020/02/14/what-changes-should-i-consider-in-my-diagnostic-approach-to-hospitalized-patients-with-community-acquired-pneumonia-cap-in-light-of-the-2019-guidelines-of-the-american-thoracic-society-ats-and-inf/ 

Anerobic coverage of aspiration pneumonia: https://pearls4peers.com/2019/07/31/should-i-routinely-select-antibiotics-with-activity-against-anaerobes-in-my-patients-with-presumed-aspiration-pneumonia/

References

  1. Mandell LA, Wunderink RG, Anzueto A. Infectious Disease Society of America/American Thoracic Society Consensus Guidelines on the Management guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007;44:S27-72. https://www.ncbi.nlm.nih.gov/pubmed/17278083
  2. Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia. Am J Respir Crit Care Med 2019;200:e45-e67. https://www.ncbi.nlm.nih.gov/pubmed/31573350

 

What changes should I consider in my treatment of hospitalized patients with community-acquired pneumonia (CAP) in light of the 2019 guidelines of the American Thoracic society (ATS) and Infectious Diseases Society of America (IDSA)?

What changes should I consider in my diagnostic approach to hospitalized patients with community-acquired pneumonia (CAP) in light of the 2019 guidelines of the American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA)?

Compared to 2007,1 the 2019 ATS/IDSA guidelines2 have 2 major “Do’s” and 2 major “Dont’s” in the diagnostic approach to CAP in hospitalized patients:

  • DO order sputum and blood cultures in patients empirically treated for methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa—in addition to those with severe CAP as in 2007.  
  • DO order rapid influenza molecular assay—in preference to antigen test— when influenza viruses are circulating in community, irrespective of pneumonia severity
  • DON’T routinely order urine antigens for pneumococcal or Legionella antigens, except in severe CAP or in the presence of suggestive epidemiological factors (eg. Legionella outbreak, recent travel)
  • DON’t routinely order serum procalcitonin to determine need for initial antibacterial therapy

Patients at risk of MRSA or P. aeruginosa include those with prior infection with the same pathogens as well as those with hospitalization and treated with parenteral antibiotics—in or out of the hospital— in the last 90 days; HCAP is no longer recognized as an entity.

The definition of severe CAP is unchanged: 1 of 2 major criteria (septic shock or respiratory failure requiring mechanical ventilation) or 3 or more of the following minor criteria or findings listed below:

  • Clinical
    • Respiratory rate ≥30 breath/min
    • Hypotension requiring aggressive fluid resuscitation
    • Hypothermia (core temperature <36 ᵒC, 96.8 ᵒF)
    • Confusion/disorientation
  • Radiographic 
    • Multilobar infiltrates
  • Laboratory 
    • Leukopenia (WBC <4,000/ul)
    • Thrombocytopenia (platelets <100,000/ul)
    • BUN ≥20 mg/dl
    • Pa02/FI02 ratio ≤250

Keep in mind that these guidelines focus on adults who are not immunocompromised or had recent foreign travel and are often based on expert opinion but low or very low quality evidence due to the dearth of properly designed studies.

Bonus Pearl: Did you know that the urine Legionella antigen only tests for L. pneumophila type I, with an overall sensitivity ranging from 45% to 100%!3,4

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References

  1. Mandell LA, Wunderink RG, Anzueto A. Infectious Disease Society of America/American Thoracic Society Consensus Guidelines on the Management guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007;44:S27-72. https://www.ncbi.nlm.nih.gov/pubmed/17278083
  2. Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia. Am J Respir Crit Care Med 2019;200:e45-e67. https://www.ncbi.nlm.nih.gov/pubmed/31573350
  3. Blazquez RM, Espinosa FJ, Martinez-Toldos CM, et al. Sensitivity of urinary antigen test in relation to clinical severity in a large outbreak of Legionella pneumonia in Spain. Eur J Clin Microbiol Infect Dis 2005;24:488-91. https://www.ncbi.nlm.nih.gov/pubmed/15997369
  4. Marlow E, Whelan C. Legionella pneumonia and use of the Legionella urinary antigen test. J Hosp Med 2009;4:E1-E2. https://www.ncbi.nlm.nih.gov/pubmed/19301376

 

 

What changes should I consider in my diagnostic approach to hospitalized patients with community-acquired pneumonia (CAP) in light of the 2019 guidelines of the American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA)?

The chest CT of my patient with “B” symptoms shows hilar mass and mediastinal lymphadenopathy, highly suspicious for lymphoma or malignancy per radiology report. Should I still consider tuberculosis (TB) as a possibility?

Absolutely! TB often mimics malignancy, particularly lymphoma, both clinically and radiographically, even when sophisticated imaging techniques are used.1  

There are ample reports of TB being confused with mediastinal lymphoma, 1-6 with several reports also stressing abdominal TB mimicking malignancy. 7-10 As early as  1949, a  NEJM autopsy study emphasized “the difficulty in differentiating primary progressive TB and some types of lymphoma” and metastatic neoplasms, clinically and radiographically.  Over half-century later, despite major advancement in imaging techniques, TB is often confused for lymphoma or malignancy.

One reason for confusing TB with lymphoma is that primary TB can involve any pulmonary lobe or segment and is often associated with hilar and mediastinal adenopathy. 1 TB may also be overlooked in the differential diagnosis of mediastinal mass that often highlights neoplasms such as lymphoma, thymoma and germ cell tumors. 3 Lack of concurrent pulmonary infiltrates in the presence of mediastinal adenopathy may also veer clinicians away from TB diagnosis. 2,3,6 Unfortunately, even more sophisticated PET/CT scans may not be able to differentiate TB from lymphoma.5,6,9

Besides chest and abdomen, TB can also mimic malignancy in cervical nodes, bones (particularly the spine), bowels, and brain.1,2,6,8,9  To make matters worse, splenomegaly 2,10 and elevated LDH 3 may also be seen with TB and TB may coexist with lymphoma and other malignancies. 7,9,11

One of the best advices I ever received from a radiologist was “Think of TB anytime you think of lymphoma.”

Bonus Pearl: Did you know that TB lymphadenitis is the most common form of extrapulmonary TB with the majority involving the mediastinum? 4

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References

  1. Tan CH, Kontoyiannis DP, Viswanathan C, et al. Tuberculosis: A benign impostor. AJR 2010;194:555-61. https://www.researchgate.net/publication/41509877_Tuberculosis_A_Benign_Impostor
  2. Smith DT. Progressive primary tuberculosis in the adult and its differentiation from lymphomas and mycotic infections. N Engl J Med 1949;241:198-202. https://www.ncbi.nlm.nih.gov/pubmed/18137399
  3. Maguire S, Chotirmall SH, Parihar V, et al. Isolated anterior mediastinal tuberculosis in an immunocompetent patient. BMC Pulm Med 2016;16:24. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4739107/
  4. Tang SS, Yang ZG, Deng W, et al. Differentiation between tuberculosis and lymphoma in mediastinal lymph nodes: evaluation with contrast-enhanced MDCT. Clin Radiol 2012;67:877-83. https://www.sciencedirect.com/science/article/abs/pii/S0009926012001079
  5. Hou S, Shen J, Tan J. Case report: Multiple systemic disseminated tuberculosis mimicking lymphoma on 18F-FDG PET/CT. Medicine 2017;96:29(e7248). https://journals.lww.com/md-journal/Pages/ArticleViewer.aspx?year=2017&issue=07210&article=00005&type=Fulltext
  6. Tian G, Xiao Y, Chen B, et al. Multi-site abdominal tuberculosis mimics malignancy on 18F-FDG PET/CT: Report of three cases. World J Gastroenterol 2010;16:4237-4242. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2932932/
  7. Dres M, Demoule A, Schmidt M, et al. Tuberculosis hiding a non-Hodgkin lymphoma “there may be more to this than meets the eye”. Resp Med Case Rep 2012;7:15-16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3920344/
  8. Banerjee Ak, Coltart DJ. Abdominal tuberculosis mimicking lymphoma in a patient with sickle cell anemia. Br J Clin Pract 1990;44:660-61. https://www.ncbi.nlm.nih.gov/pubmed/2102179?dopt=Abstract
  9. Gong Y, Li S, Rong R, et al. Isolated gastric varices secondary to abdominal tuberculosis mimicking lymphoma: a case report. Gastroenterology 109;19:78. https://www.ncbi.nlm.nih.gov/pubmed/31138138
  10. Uy AB, Garcia Am Manguba A, et al. Tuberculosis: the great lymphoma pretender. Int J Cancer Res Mol Mech 2016; 2(1):doi http://dx.doi.org/10.16966/2381-3318.123
  11. Nayanagari K, Rani R, Bakka S, et al. Pulmonary tuberculosis with mediastinal lymphadenopathy and superior veno caval obstruction, mimicking lung malignancy: a case report. Int J Sci Study 2015;2:211-14. https://www.ncbi.nlm.nih.gov/pubmed/31138138
The chest CT of my patient with “B” symptoms shows hilar mass and mediastinal lymphadenopathy, highly suspicious for lymphoma or malignancy per radiology report. Should I still consider tuberculosis (TB) as a possibility?

My patient with COPD exacerbation has an elevated venous blood PCO2. How accurate is the peripheral venous blood gas PC02 in patients with hypercarbia?

Short answer: Not as accurate as we might like! An elevated venous pC02 is a good indicator of the presence of arterial hypercarbia but beyond that if you really want to know what the arterial pC02 is in your patient with hypercarbia, you should get an arterial blood gas (ABG).

 
A meta-analysis of studies involving patients with COPD presenting to the emergency department (ED) found a good agreement for pH and bicarbonate values between arterial and venous blood gases but not for pC02 or p02 (1). More specifically, the 95% limit of agreement varied widely from -17 to +26 mmHg between venous and arterial pC02 (average difference ~6.0 mm). In the same study, a venous pC02 of ~45 mmHg or less correctly identified patients who were hypercarbic based on ABG. Similar results have been reported by other studies involving patients with COPD exacerbation (2,3).

 
Another meta-analysis involving all comers (COPD and non-COPD patients) concluded that venous pC02 should not be used as a substitute for arterial pC02 when accurate pC02 is required (4). In fact, they emphasized that venous pC02 was not always greater than arterial pC02!

 
Bonus pearl: Did you know that an unexpectedly low bicarbonate level in a patient with COPD and CO2 retention should alert us to the possibility of concurrent metabolic acidosis (eg, due to lactic acidosis, uremia)?

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References
1. Lim BL, Kelly AM. A meta-analysis on the utility of peripheral venous blood gas analyses in exacerbations of chronic obstructive pulmonary disease in the emergency department. Eur J Emerg Med 2010;17:246-48. https://journals.lww.com/euro-emergencymed/Abstract/2010/10000/A_meta_analysis_on_the_utility_of_peripheral.2.aspx
2. McCanny P, Bennett K, Staunton P, et a. Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease. Am J Emerg Med 2012;30:896-900. https://www.sciencedirect.com/science/article/abs/pii/S0735675711002865
3. McKeevere TM, Hearson G, Housely G, et al. Using venous blood gas analysis in the assessment of COPD exacerbations: a prospective cohort study. Thorax 2016;71:210-15. https://www.researchgate.net/publication/285545995_Using_venous_blood_gas_analysis_in_the_assessment_of_COPD_exacerbations_A_prospective_cohort_study
4. Byrne AL, Bennett M, Chatterji R, et al. Peripheral venous and arterial blood gas analysis in adults:are they comparable? A systematic review and meta-analysis. Respirology 2014;19:168-75. https://onlinelibrary.wiley.com/doi/full/10.1111/resp.12225

My patient with COPD exacerbation has an elevated venous blood PCO2. How accurate is the peripheral venous blood gas PC02 in patients with hypercarbia?

Should I routinely treat my patients with acute COPD exacerbation with antibiotics?

The answer is “NO”! With an estimated 20% to 50% of acute chronic obstructive pulmonary disease (COPD) exacerbations attributed to noninfectious factors (1,2), routine inclusion of antibiotics in the treatment of this condition is not only unnecessary but potentially harmful.

 
Although the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines recommends the use of antibiotics in patients who have dyspnea, increased sputum volume, and increased sputum purulence—or at least 2 of these 3 criteria when sputum purulence is one of them (3)—, these recommendations are not based on robust evidence and have not been widely corroborated (2,4-6).

 
That’s why the findings of a 2019 New England Journal of Medicine study (PACE) supporting the use of serum C-reactive protein (CRP) as an adjunctive test in COPD exacerbation is particularly welcome (1). In this multicenter randomized controlled trial performed in the U.K., the following CRP guidelines (arrived from prior studies) were provided to primary care clinicians to be used as part of their decision making in determining which patients with COPD exacerbation may not need antibiotic therapy:
• CRP less than 20 mg/L: Antibiotics unlikely to be beneficial
• CRP 20-40 mg/L: Antibiotics may be beneficial, mainly if purulent sputum is present
• CRP greater than 40 mg/L: Antibiotics likely to be beneficial

 
Adoption of these guidelines resulted in significantlly fewer patients being placed on antibiotics without evidence of harm over a 4-week follow-up period (1).  Despite its inherent limitations (eg, single country, outpatient setting), CRP testing may be a step in the right direction in curbing unnecessary use of antibiotics in COPD exacerbation.  

 

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References
1. Butler CC, Gillespie D, White P, et al. C-reactive protein testing to guide antibiotic prescribing for COPD exacerbations. N Engl J Med 2019;381:111-20. https://www.ncbi.nlm.nih.gov/pubmed/31291514
2. Llor C, Moragas A, Hernandez S, et al. Efficacy of antibiotic therapy for acute exacerbations of mild to moderate chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2012;186:716-23. https://www.ncbi.nlm.nih.gov/pubmed/22923662
3. Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease. GOLD, 2019 (http://www.goldcopd.org).
4. Brett AS, Al-Hasan MN. COPD exacerbations—A target for antibiotic stewardship. N Engl J Med 2018;381:174-75. https://www.ncbi.nlm.nih.gov/pubmed/31291521
5. Miravitlles M, Moragas A, Hernandez S, et al. Is it possible to identify exacerbations of mild to moderate COPD that do not require antibiotic treatment? Chest 2013;144:1571-7. https://www.ncbi.nlm.nih.gov/pubmed/23807094
6. Van Vezen P, Ter Riet G, Bresser P, et al. Doxycycline for outpatient-treated acute exacerbations of COPD: a randomized double-blind placebo-controlled trial. Lancet Respir Med 2017;5:492-9. https://www.ncbi.nlm.nih.gov/pubmed/28483402

Should I routinely treat my patients with acute COPD exacerbation with antibiotics?