How long should I expect Legionella urine antigen test to remain positive after diagnosis of legionnaire’s disease in my patient with pneumonia?

The urine antigen test for detection of Legionnaire’s disease (LD) can remain positive for weeks or months after initial infection. So a positive test in a patient with pneumonia may not just be suggestive of an acute infection but also the diagnosis of LD during recent weeks or months (1,2).

In a study of Legionella urine antigen detection as a function of days after onset of symptoms, 11 of 11 (100%) patients tested remained positive after day 14 (1). In the same study, 10 of 23 (43%) patients excreted antigen for 42 days or longer following initiation of therapy, with some patients remaining positive for more than 200 days!

In another study involving 61 patients with Legionella pneumophila pneumonia, 25% excreted Legionella antigen for 60 or more days (2). Longer duration of antigen excretion was significantly associated with immunosuppressed patients in whom the time to resolution of fever was > 72 h.

The long duration of excretion of Legionella antigen in urine following LD is not surprising. Pneumococcal pneumonia has also been associated with prolonged antigen excretion, some for as long as 6 months after diagnosis of pneumonia (3). It is thought that some microbial polysaccharides may be degraded very slowly or not at all by mammalian tissues which could explain their prolonged appearance in the urine long after active infection has resolved (1).

Bonus pearl: Did you know that the sensitivity of Legionella urinary antigen for LD varies from 94% for travel-associated infections to 76%-87% for community-acquired infection, and to as low as ~45% for nosocomially-acquired infections (4)?

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References

  1. Kohler RB, Winn WC, Wheat J. Onset and duration of urinary antigen excretion in Legionnaires disease. J Clin Microbiol 1984;20:605-7. https://pubmed.ncbi.nlm.nih.gov/6490846/
  2. Sopena N, Sabria M, Pedro-Bolet ML, et al. Factors related to persistence of Legionella urinary antigen excretion in patients with legionnaire’s disease. Eur J Clin Microbiol Infect Dis 2002;21:845-48. https://europepmc.org/article/med/12525918
  3. Andreo F, Prat C, Ruiz-Manzano J, et al. Persistence of Streptococcus pneumoniae urinary antigen excretion after pneumococcal pneumonia. Eur J Clin Microbiol Infect Dis 2009;28:197-201. https://pubmed.ncbi.nlm.nih.gov/18830727/
  4. Helbig JH, Uldum SA, Bernander S, et al. Clinical utility of urinary antigen detection for diagnosis of community-acquired, travel-associated, and nosocomial Legionnaire’s disease. Clin Microbiol 2003;41:838-40. https://pubmed.ncbi.nlm.nih.gov/12574296/

 

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!

How long should I expect Legionella urine antigen test to remain positive after diagnosis of legionnaire’s disease in my patient with pneumonia?

How often is Covid-19 in hospitalized patients complicated by bacterial infection?

Despite frequent use of empiric antibiotics in hospitalized patients with Covid-19,current data suggests a low rate of documented bacterial co-infection (BCI) in such patients. In fact, the overall reported rate of BCI in hospitalized patients with Covid-19 is generally no greater than 10%.1-3   It’s quite likely that most patients with Covid-19 and chest radiograph changes solely have a coronavirus (SARS-CoV-2) lung infection,4 particularly early in the course of the disease.  

A meta-analysis involving 30 studies (primarily retrospective) found that overall 7% of hospitalized Covid-19 patients had a laboratory-confirmed BCI with higher proportion among ICU patients (14%).Mycoplasma pneumoniae was the most common (42% of BCIs), followed by Pseudomonas aeruginosa and H. influenzae.  Notably, diagnosis of M. pneumoniae infection was based on antibody testing for IgM, which has been associated with false-positive results. Other caveats include lack of a uniform definition of respiratory tract infection among studies and potential impact of concurrent or prior antibiotic therapy on the yield of bacteriologic cultures. 5,6

A low prevalence of BCI was also found in a UK study involving 836 hospitalized Covid-19 patients: 3.2% for early BCI (0-5 days after admission) and 6.1% throughout hospitalization, including hospital-acquired infections.Staphylococcus aureus was the most common respiratory isolate among community-acquired cases, while Pseudomonas spp. was the predominant healthcare associated respiratory isolate.  Similarly, S. aureus. and Streptococcus pneumoniae were the most commonly isolated organisms from blind bronchoalveolar lavage of critically ill patients with Covid-19 during their first 5 days of admission, while gram-negative bacilli became dominant later during the hospitalization.8

The discordance between high rates of antibiotic treatment and confirmed bacterial co-infection in Covid-19 patients is likely a reflection of the difficulty in distinguishing Covid-19 pneumonia from bacterial pneumonia based on clinical or radiographic findings alone.

We need better tests to help distinguish bacterial vs Covid-19 pneumonia. Some have suggested using a low serum procalcitonin to help guide the withholding of or early discontinuation of antibiotics, especially in less severe Covid-19 cases. Formal studies of the accuracy of procalcitonin in Covid-19 are needed to test this hypothesis, given its suboptimal sensitivity in bacterial community-acquired pneumonia. 

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Reference

  1. Stevens RW, Jensen K, O’Horo JC, et al. Antimicrobial prescribing practices at a tertiary-care center in patients diagnosed with COVID-19 across the continuum of care. Infect Control Hosp Epidemiology 2020. https://reference.medscape.com/medline/abstract/32703323
  2. Lansbury L, Lim B, Baskaran V, et al. Co-infections in people with COVID-19: a systematic review and meta-analysis. J Infect 2020;81:266-75. https://pubmed.ncbi.nlm.nih.gov/32473235/
  3. Rawson TM, Moore LSP, Zhu N. Bacterial and fungal co-infection in individuals with coronavirus: A rapid review to support COVID-19 antimicrobial prescribing. Clin Infect Dis 2020 (Manuscrpit published online ahead of print 2 June ). Doi:10.1093/cid/ciaa530.https://pubmed.ncbi.nlm.nih.gov/32358954/
  4. Metlay JP, Waterer GW. Treatment of community-acquired pneumonia during the coronavirus 2019 (COVID-19) pandemic. Ann Intern Med 2020; 173:304-305. https://pubmed.ncbi.nlm.nih.gov/32379883/
  5. Chang CY, Chan KG. Underestimation of co-infections in COVID-19 due to non-discriminatory use of antibiotics. J Infect 2020;81:e29-30. https://pubmed.ncbi.nlm.nih.gov/32628960/
  6. Rawson TM, Moore LSP, Zhu N, et al. Bacterial pneumonia in COVID-19 critically ill patients: A case series. Reply letter. Clin Infect Dis 2020. https://academic.oup.com/cid/advance-
  7. Hughes S, Troise O, Donaldson H, et al. Bacterial and fungal coinfection among hospitalized patients with COVID-19: a retrospective cohort study in a UK secondary-care setting. Clin Microbiol Infect 2020. https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(20)30369-4/fulltext
  8. Dudoignon E, Camelena F, Deniau B, et al. Bacterial pneumonia in COVID-19 critically ill patients: A case series. Clin Infect Dis 2020. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7337703/

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!

How often is Covid-19 in hospitalized patients complicated by bacterial infection?

How might categorizing severity of illness help in the management of my patient with Covid-19?

Although the criteria for Covid-19 severity of illness categories may overlap at times or vary across guidelines and clinical trials, I have found those published in the National Institute of Health (USA) Covid-19 Treatment Guidelines most useful and uptodate.1  Keep in mind that the primary basis for severity categories in Covid-19 is the degree by which it alters pulmonary anatomy and physiology and respiratory function (see my table below).

The first question to ask when dealing with Covid-19 patients is whether they have any signs or symptoms that can be attributed to the disease (eg, fever, cough, sore throat, malaise, headache, muscle pain, lack of sense of smell). In the absence of any attributable symptoms, your patient falls into “Asymptomatic” or “Presymptomatic” category.  These patients should be monitored for any new signs or symptoms of Covid-19 and should not require additional laboratory testing or treatment.

If symptoms of Covid-19 are present (see above), the next question to ask is whether the patient has any shortness of breath or abnormal chest imaging. If neither is present, the illness can be classified as “Mild” with no specific laboratory tests or treatment indicated in otherwise healthy patients. These patients may be safely managed in ambulatory settings or at home through telemedicine or remote visits. Those with risk factors for severe disease (eg, older age, obesity, cancer, immunocompromised state), 2 however, should be closely monitored as rapid clinical deterioration may occur.

Once lower respiratory tract disease based on clinical assessment or imaging develops, the illness is no longer considered mild. This is a good time to check a spot 02 on room air and if it’s 94% or greater at sea level, the illness qualifies for “Moderate” severity. In addition to close monitoring for signs of progression, treatment for possible bacterial pneumonia or sepsis should be considered when suspected. Corticosteroids are not recommended here and there are insufficient data to recommend either for or against the use of remdesivir in patients with mild/moderate Covid-19.

Once spot 02 on room air drops below 94%, Covid-19 illness is considered “Severe”; other parameters include respiratory rate >30, Pa02/Fi02 < 300 mmHg or lung infiltrates >50%. Here, patients require further evaluation, including pulmonary imaging, ECG, CBC with differential and a metabolic profile, including liver and renal function tests. C-reactive protein (CRP), D-dimer and ferritin are also often obtained for their prognostic value. These patients need close monitoring, preferably in a facility with airborne infection isolation rooms.  In addition to treatment of bacterial pneumonia or sepsis when suspected, consideration should also be given to treatment with corticosteroids. Remdesivir is recommended for patients who require supplemental oxygen but whether it’s effective in those with more severe hypoxemia (eg, those who require oxygen through a high-flow device, noninvasive or invasive mechanical ventilation or extracorporeal membrane oxygenation-ECMO) is unclear. Prone ventilation may be helpful here in patients with refractory hypoxemia as long as it is not used to avoid intubation in those who otherwise require mechanical ventilation.

“Critical” illness category is the severest forms of Covid-19 and includes acute respiratory distress syndrome (ARDS), septic shock, cardiac dysfunction and cytokine storm. In addition to treatment for possible bacterial pneumonia or sepsis when suspected, corticosteroids and supportive treatment for hemodynamic instability and ARDS, including prone ventilation, are often required. The effectiveness of remdesivir in patients with severe hypoxemia (see above) is unclear at this time.

 

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 References

  1. NIH COVID-19 Treatment Guidelines. https://www.covid19treatmentguidelines.nih.gov/. Accessed Aug 27, 2020.
  2. CDC. Covid-19.  https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/people-with-medical-conditions.html/. Accessed Aug 27, 2020.  

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!

 

How might categorizing severity of illness help in the management of my patient with Covid-19?