My patient with diabetes mellitus is now admitted with pneumonia. Does diabetes increase the risk of pneumonia requiring hospitalization?

The weight of the evidence to date suggests that diabetes mellitus (DM) does increase the risk of pneumonia-related hospitalization.1-3

A large population-based study involving over 30,000 patients found an adjusted relative risk (RR) of hospitalization with pneumonia of 1.26 (95% C.I 1.2-1.3) among patients with DM compared to non-diabetics.  Of note, the risk of pneumonia-related hospitalization was significantly higher in type 1 as well as type 2 DM and among patients whose A1C level was ≥9.1  Another population-based study found a high prevalence of DM (25.6%) in patients hospitalized with CAP, more than double that in the population studied.2  A 2016 meta-analysis of observational studies also found increased incidence of respiratory tract infections among patients with diabetes (OR 1.35, 95% C.I. 1.3-1.4).

Not only does DM increase the risk of pneumonia-related hospitalization, but it also appears to adversely affect its outcome with increased in-hospital mortality.2 Among patients with type 2 DM,  excess mortality has also been reported at 30 days, 90 days and 1 year following hospitalization for pneumonia. 4,5 More specifically, compared to controls with CAP, 1 year mortality of patients with DM was 30% (vs 17%) in 1 study. 4

Potential reasons for the higher incidence of pneumonia among patients with DM include increased risk of aspiration (eg, in the setting of gastroparesis, decreased cough reflex), impaired immunity (eg, chemotaxis, intracellular killing), pulmonary microangiopathy and coexisting morbidity. 1,3,5,6

Bonus Pearl: Did you know that worldwide DM has reached epidemic levels, such that if DM were a nation, it would surpass the U.S. as the 3rd most populous country! 7

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References

  1. Kornum JB, Thomsen RW, RUS A, et al. Diabetes, glycemic control, and risk of hospitalization with pneumonia. A population-based case-control study. Diabetes Care 2008;31:1541-45. https://www.ncbi.nlm.nih.gov/pubmed/17595354
  2. Martins M, Boavida JM, Raposo JF, et al. Diabetes hinders community-acquired pneumonia outcomes in hospitalized patients. BMJ Open Diabetes Research and Care 2016;4:e000181.doi:10.1136/bmjdrc-2015000181. https://drc.bmj.com/content/4/1/e000181
  3. Abu-Ahour W, Twells L, Valcour J, et al. The association between diabetes mellitus and incident infections: a systematic review and meta-analysis of observational studies. BMJ Open Diabetes Research and Care 2017;5:e000336. https://drc.bmj.com/content/5/1/e000336. 
  4. Falcone M, Tiseo G, Russo A, et al. Hospitalization for pneumonia is associated with decreased 1-year survival in patients with type 2 diabetes. Results from a prospective cohort study. Medicine 2016;95:e2531. https://www.ncbi.nlm.nih.gov/pubmed/26844461
  5. Kornum JB, Thomsen RW, Rus A, et al. Type 2 diabetes and pneumonia outcomes. A population-based cohort study. Diabetes Care 2007;30:2251-57. https://www.ncbi.nlm.nih.gov/pubmed/17595354
  6. Koziel H, Koziel MJ. Pulmonary complications of diabetes mellitus. Pneumonia. Infect Dis Clin North Am 1995;9:65-96. https://www.ncbi.nlm.nih.gov/pubmed/7769221
  7. Zimmet PZ. Diabetes and its drivers: the largest epidemic in human history? Clinical Diabetes and Endocrinology 2017;3:1 https://clindiabetesendo.biomedcentral.com/articles/10.1186/s40842-016-0039-3  

 

My patient with diabetes mellitus is now admitted with pneumonia. Does diabetes increase the risk of pneumonia requiring hospitalization?

My patient with sepsis and bacteremia has an extremely high serum Creatine kinase (CK) level. Can his infection be causing rhabdomyolysis?

 Absolutely! Although trauma, toxins, exertion, and medications are often listed as common causes of rhabdomyolysis, infectious etiologies should not be overlooked as they may account for 5% to 30% or more of rhabdomyolysis cases (1,2).

 

Rhabdomyolysis tends to be associated with a variety of infections, often severe, involving the respiratory tract, as well as urinary tract, heart and meninges, and may be caused by a long list of pathogens (1).  Among bacterial causes, Legionella sp. (“classic” pathogen associated with rhabdomyolysis), Streptococcus sp. (including S. pneumoniae), Salmonella sp, Staphylococcus aureus, Francisella tularensis have been cited frequently (3).  Some series have reported a preponderance of aerobic gram-negatives such as Klebsiella sp., Pseudomonas sp. and E. coli  (1,2).   Among viral etiologies, influenza virus, human immunodeficiency virus, and coxsackievirus are commonly cited (2,3).  Fungal and protozoal infections (eg, malaria) may also be associated with rhabdomyolysis (5).

 

So how might sepsis cause rhabdomyolysis? Several potential mechanisms have been implicated, including tissue hypoxemia due to sepsis, direct muscle invasion by pathogens (eg, S. aureus, streptococci, Salmonella sp.), toxin generation (eg, Legionella), cytokine-mediated muscle cell toxicity (eg, aerobic gram-negatives) as well as muscle ischemia due to shock (1,5).

 

Bonus Pearl: Did you know that among patients with HIV infection, infections are the most common cause (39%) of rhabdomyolysis (6)? 

 

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References

 

1. Kumar AA, Bhaskar E, Shantha GPS, et al. Rhabdomyolysis in community acquired bacterial sepsis—A retrospective cohort study. PLoS ONE 2009;e7182. Doi:10.1371/journa.pone.0007182. https://www.ncbi.nlm.nih.gov/pubmed/19787056.

2. Blanco JR, Zabaza M, Sacedo J, et al. Rhabdomyolysis of infectious and noninfectious causes. South Med J 2002;95:542-44. https://www.ncbi.nlm.nih.gov/pubmed/12005014

3. Singh U, Scheld WM. Infectious etiologies of rhabdomyolysis:three case reports and review. Clin Infect Dis 1996;22:642-9. https://www.ncbi.nlm.nih.gov/pubmed/8729203

4. Shih CC, Hii HP, Tsao CM, et al. Therapeutic effects of procainamide on endotoxin-induced rhabdomyolysis in rats. PLOS ONE 2016. Doi:10.1371/journal.pone.0150319. https://www.ncbi.nlm.nih.gov/pubmed/26918767

5. Khan FY. Rhabdomyolysis: a review of the literature. NJM 2009;67:272-83. http://www.njmonline.nl/getpdf.php?id=842

6. Koubar SH, Estrella MM, Warrier R, et al. Rhabdomyolysis in an HIV cohort: epidemiology, causes and outcomes. BMC Nephrology 2017;18:242. DOI 10.1186/s12882-017-0656-9. https://bmcnephrol.biomedcentral.com/track/pdf/10.1186/s12882-017-0656-9

My patient with sepsis and bacteremia has an extremely high serum Creatine kinase (CK) level. Can his infection be causing rhabdomyolysis?

Is there a connection between trehalose, a natural sugar found in many foods, and Clostridioides difficile disease (CDD)?

There is experimental and epidemiological evidence that trehalose in the diet may enhance the virulence of the epidemic strains (eg. Ribotype 027) of C. difficile (1). 
Many of us may not be familiar with trehalose. It’s a disaccharide composed of 2 glucose molecules and found widely in nature, including bacteria, fungi (eg mushrooms, Brewer’s yeast), plants, insects, other invertebrates, but not vertebrates (2).

Since its approval by the FDA as a natural food additive in 2000, trehalose is increasingly used for its unique properties (including flavor enhancer and moisture stabilizer) in a variety of foods, including ice cream, pasta, ground beef, and sushi. Although in humans trehalose is enzymatically broken down to glucose by the brush borders of intestinal mucosa, intact trehalose is also found in the lower GI tract where C. difficile thrives.

 
In a series of intriguing experiments involving the interaction between trehulose and C. difficile published in Nature in 2018, Collins et al found that RT027 strain of C. difficile had acquired unique mechanisms to metabolize low concentrations of trehalose and that dietary trehalose increased its virulence associated with high mortality in a mouse model of infection even in the absence of antibiotic exposure. They further demonstrated that when human diet was simulated (eg, at concentrations suggested in ice cream), trehalose levels in the cecum of the mice were sufficient to induce production of the enzyme phosphotrehalase by the same strain in vitro by over 400X in the absence of antibiotics and by over 1000X in the presence of antibiotics. Similar results were found in the ileostomy fluid samples of 2 of 3 volunteers consuming normal diet (1). 

 
Equally fascinating is the epidemiological evidence that the timelines of trehalose adoption as a food additive in 2000, subsequent uptick in the number CDDs in the US, as well as the spread of RT027 strain in many countries seem to overlap (1).

 
These observations may at least partially explain the frequently severe nature of CDD during the past 2 decades as well why a significant proportion (up to a-third) of patient with CDD appear to have no recent exposure to antibiotics or hospitalization (3-5).  An epidemiological study examining the dietary habits of patients with CDD without apparent risk factors is in order. Stay tuned!

 
Bonus Pearl: Did you know that trehalose is classified as “generally regarded as safe” (GRAS)  natural food additive by the FDA and may be listed as “added sugar” or “natural flavor” on the food packaging?

 

References
1. Collins J, Robinson C, Danhof H, et al. Dietary trehalose enhances virulence of epidemic Clostridium difficile. Nature 2018;553;291-96. https://www.nature.com/articles/nature25178
2. Avonce N, Mendoza-Vargas A, Morett E, et al. Insights on the evolution of trehalose biosynthesis. BMC Evol Biol 2006;6:109. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1769515/
3. Wilcox MH, Mooney L, Bendall R, Settle CD et al. A case-control study of community-associated Clostridium difficile infection. J Antimicrob Chemother 2008;62:388-96. https://www.researchgate.net/publication/5419268_A_case-control_study_of_community-associated_Clostridium_difficile_infection
4. Severe Clostridium difficile-associated disease in populations previously at low risk. MMWR2005;54:1201-5. https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5447a1.htm
5. Halvorson SAC, Cedfeldt AS, Hunter AJ. Fulminant, non-antibiotic associated Clostridium difficile colitis following Salmonella gastroenteritis. J Gen Intern Med 2010;26:95-7.

 

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Is there a connection between trehalose, a natural sugar found in many foods, and Clostridioides difficile disease (CDD)?

Is meropenem a good choice of antibiotic for treatment of my patient’s intraabdominal infection involving enterococci?

Although meropenem is a broad spectrum antibiotic that covers many gram-negative and gram-positive organisms as well as anaerobes, its activity against enterococci is generally poor and leaves much to be desired.

In a study of ampicillin-sensitive E. faecalis isolates from hospitalized patients, only 36% of isolates were considered susceptible (MIC≤4 mg/L); activity against E. faecium isolates was similarly poor.1 Several other studies have reported the suboptimal activity of meropenem against both E. faecalis and E. faecium, 2-4 with susceptibility rates as low as 8.6% depending on the MIC break point used.3

A popular textbook and a handbook on infectious diseases also do not recommend the use of meropenem for treatment of enterococcal infections. 5,6

Of interest, the package insert states that meropenem is indicated for complicated skin and soft tissue infections due to a variety of organisms, including E. faecalis (vancomycin-susceptible isolates only), but not for complicated intra-abdominal infections or meningitis due this organism.7

In our patient with intraabdominal infection,  we may consider piperacillin-tazobactam instead.  Piperacillin-tazobactam is a broad spectrum antibiotic with excellent coverage against anaerobes and ampicillin-susceptible E. faecalis.1,8  

 

References

  1. Endtz HP, van Dijk WC, Verbrugh HA, et al. Comparative in-vitro activity of meropenem against selected pathogens from hospitalized patients in the Netherlands. J Antimicrob Chemother 1997;39:149-56. https://www.ncbi.nlm.nih.gov/pubmed/9069534
  2. Pfaller MA, Jones RN. A review of the in vitro activity of meropenem and comparative antimicrobial agents tested against 30,254 aerobic and anaerobic pathogens isolated world wide. Diag Microbiol Infect Dis 1997;28:157-63. https://www.ncbi.nlm.nih.gov/pubmed/9327242
  3. Hallgren A, Abednazari H, Ekdahl C, et al. Antimicrobial susceptibility patterns of enterococci in intensive care units in Sweden evaluated by different MIC breakpoint systems. J Antimicrob Chemother 2001;48:53-62. https://www.ncbi.nlm.nih.gov/pubmed/11418512
  4. Hoban DJ, Jones RN, Yamane N, et al. In vitro activity of three carbapenem antibiotics comparative studies with biapenem (L-627), imipenem, and meropenem against aerobic pathogens isolated worldwide. Diag Microbiol Infect Dis 993;17:299-305.https://www.ncbi.nlm.nih.gov/pubmed/8112045
  5. Chambers HF. Carbapenem and monobactams. In Mandell GL et al. eds. Principles and practice of infectious diseases. 2010, pp 341-45.
  6. Cunha CB, Cunha BA. Antibiotic essentials. 2017, pp 689-91.
  7. Meropenem.http://online.lexi.com/lco/action/doc/retrieve/docid/patch_f/7253?searchUrl=%2Flco%2Faction%2Fsearch%3Fq%3Dmeropenem%26t%3Dname
  8. Perry CM, Markham A. Piperacillin/tazobactam. Drugs 1999;57:805-43. https://link.springer.com/article/10.2165%2F00003495-199957050-00017

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Is meropenem a good choice of antibiotic for treatment of my patient’s intraabdominal infection involving enterococci?

Should my patient with COPD and recurrent exacerbations undergo evaluation for antibody deficiency?

Although there are no consensus guidelines on when to evaluate patients with COPD for antibody deficiency, we should at least consider this possibility in patients with recurrent exacerbations despite maximal inhaled therapy (long-acting beta-2 agonist-LABA, long-acting muscarinic antagonist-LAMA and inhaled corticosteroids).1

Couple of retrospective studies of common variable immunodeficiency (CVID) in patients with COPD have reported a prevalence ranging from 2.4% to 4.5%. 1 In another study involving 42 patients thought to have had 2 or more moderate to severe COPD exacerbations per year—often despite maximal inhaled therapy— 29 were diagnosed  with antibody deficiency syndrome, including 20 with specific antibody deficiency (SAD), 8 with CVID and 1 with selective IgA deficiency.2  Although systemic corticosteroids may lower IgG and IgA levels, the majority of the patients in this study were not taking any corticosteroids at the time of their evaluation.

In another study involving patients undergoing lung transplantation, pre-transplant mild hypogammaglobulinemia was more prevalent among those with COPD (15%) compared to other lung conditions (eg, cystic fibrosis), independent of corticosteroid use.3  A favorable impact of immunoglobulin therapy or chronic suppressive antibiotics on reducing recurrent episodes of COPD exacerbation in patients with antibody deficiency has also been reported, supporting the clinical relevance of hypogammaglobulinemia in these patients. 2,4 

Remember that even normal quantitative serum immunoglobulin levels (IgG, IgA, and IgM) do not necessarily rule out antibody deficiency. Measurement of IgG subclasses, as well as more specific antibodies, such as those against pneumococcal polysaccharides may be required for further evaluation.

See a related pearl at https://pearls4peers.com/2015/07/12/my-65-year-old-patient-has-had-several-bouts-of-bacterial-pneumonia-in-the-past-2-years-her-total-serum-immunoglobulins-are-within-normal-range-could-she-still-be-immunodeficient/.

Contributed in part by Sydney Montesi, MD, Mass General Hospital, Boston, MA.

References

  1. Berger M, Geng B, Cameron DW, et al. Primary immune deficiency diseases as unrecognized causes of chronic respiratory disease. Resp Med 2017;132:181-188. https://www.sciencedirect.com/science/article/pii/S0954611117303554
  2. McCullagh BN, Comelias AP, Ballas ZK, et al. Antibody deficiency in patients with frequent exacerbations of chronic obstructive pulmonary disease (COPD). PLoS ONE 2017; 12: e0172437. https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0172437
  3. Yip NH, Lederer DJ, Kawut SM, et al. Immunoglobulin G levels before and after lung transplantation 2006;173:917-21.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2662910/
  4. Cowan J, Gaudet L, Mulpuru S, et al. A retrospective longitudinal within-subject risk interval analysis of immunoglobulin treatment for recurrent acute exacerbation of chronic obstructive pulmonary disease. PLoS ONE 2015;10:e0142205. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0142205

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Should my patient with COPD and recurrent exacerbations undergo evaluation for antibody deficiency?

Should I choose a bactericidal over bacteriostatic antibiotic in the treatment of my patient with pneumonia complicated by bacteremia?

You don’t have too!  Although “bacteriostatic” antibiotics have traditionally been regarded as inferior to “bactericidal” antibiotics in the treatment of serious infections, a 2018 “myth busting” systemic literature review1 concluded that bacteriostatic antibiotics are just as effective against a variety of infections, including pneumonia, non-endocarditis bacteremia, skin and soft tissue infections and genital infections; no conclusion can be made in regards to endocarditis or bacterial meningitis, however, due insufficient clinical evidence.1-3

Interestingly, most of the studies included in the same systemic review showed that bacteriostatic antibiotics were more effective compared to bactericidal antibiotics.1 So, for most infections in hospitalized patients, including those with non-endocarditis bacteremia, the choice of antibiotic among those that demonstrate in vitro susceptibility should not be based on their “cidal” vs “static” label.

Such conclusion should not be too surprising since the definition of bacteriostatic vs bactericidal is based on arbitrary in vitro constructs and not validated by any available in vivo data. In addition, static antibiotics may kill bacteria as rapidly as cidal antibiotics in vitro at higher antibiotic concentrations.3

Another supportive evidence is a 2019 study finding similar efficacy of sequential intravenous-to-oral outpatient antibiotic therapy for MRSA bacteremia compared to continued IV antibiotic therapy despite frequent use of bacteriostatic oral antibiotics (eg, linezolid, clindamycin and doxycycline). 4

 

References

  1. Wald-Dickler N, Holtom P, Spellberg B. Busting the myth of “static vs cidal”: as systemic literature review. Clin Infect Dis 2018;66:1470-4. https://academic.oup.com/cid/article/66/9/1470/4774989
  2. Steigbigel RT, Steigbigel NH. Static vs cidal antibiotics. Clin Infect Dis 2019;68:351-2. https://academic.oup.com/cid/article-abstract/68/2/351/5067395
  3. Wald-Dickler N, Holtom P, Spellberg B. Static vs cidal antibiotics; reply to Steigbigel and Steigbigel. Clin Infect Dis 2019;68:352-3. https://academic.oup.com/cid/article-abstract/68/2/352/5067396?redirectedFrom=fulltext
  4. Jorgensen SCJ, Lagnf AH, Bhatia S, et al. Sequential intravenous-to-oral outpatient antbiotic therapy for MRSA bacteraemia: one step closer.  J Antimicrob Chemother 2019;74:489-98.  https://www.ncbi.nlm.nih.gov/pubmed/30418557

 

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Should I choose a bactericidal over bacteriostatic antibiotic in the treatment of my patient with pneumonia complicated by bacteremia?

When should I consider prophylaxis for Pneumocystis pneumonia (PCP) in my patient on prednisone?

It is generally recommended that patients on ≥20 mg of daily prednisone (or its equivalent) for ≥1 month be considered for PCP prophylaxis. 1

Couple of studies in 1990s helped define the dose and duration of corticosteroids (CS) that should prompt PCP prophylaxis. A Mayo Clinic study of patients without AIDS found that a median daily CS dose of 30 mg of prednisone or equivalent—with 25% of patients receiving as little as 16 mg of prednisone daily— was associated with PCP.The median duration of CS therapy before PCP was 12 weeks. A similar study found a mean CS dose of 33 mg of prednisone or equivalent with mean duration of 7 months (range 1-154 months) among patients with PCP without AIDS. 3

A 2018 retrospective study4  of patients with rheumatic diseases receiving prolonged high-dose CS therapy (≥30 mg prednisone for ≥4 weeks) found that PCP prophylaxis with trimethoprim/sulfamethoxazole (TMP/STX) resulted in 93% reduction in the incidence of PCP with an overall number needed to treat (NNT) of 52. It was suggested that PCP prophylaxis could be discontinued in patients receiving < 15 mg of prednisone daily.

Bonus Pearl: Did you know that TMP/STX may be given either as double-strength 3x/week or single-strength daily? 5,6

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References

1. Limper AH, Knox KS, Sarosi SA, et al. An official American Thoracic Society statement: Treatment of fungal infections in adult pulmonary and critical care patients. Am J Respir Crit Care Med 2011;183:96-128. https://www.ncbi.nlm.nih.gov/pubmed/21193785

2. Yale SH, Limper AH. Pneumocystis carinii pneumonia in patients without acquired immunodeficiency syndrome: associated illness and prior corticosteroid therapy. Mayo Clin Proc 1996;71:5-13. https://www.sciencedirect.com/science/article/abs/pii/S0025619611649148

3. Arend SM, Kroon FP, van’t Wout JW. Pneumocystis carinii pneumonia in patients without AIDS, 1980 through 1993: An analysis of 78 cases. Arch Intern Med 1995;155:2436-2441. https://www.ncbi.nlm.nih.gov/pubmed/7503602

4. Park JW, Curtis JR, Moon J, et al. Prophylactic effect of trimethoprim-sulfamethoxazole for Pneumocystis pneumonia in patients with rheumatic diseases exposed to prolonged high-dose glucocorticoieds. Ann Rheum Dis 2018;77:664-9. https://www.ncbi.nlm.nih.gov/pubmed/29092853

5. Anevlavis S, Kaltsas K, Bouros D. Prophylaxis for pneumocystis pneumonia (PCP) in non-HIV infected patients. PNEUMON 2012;25, October-December.http://www.pneumon.org/assets/files/789/file483_273.pdf

6. Stern A, Green H, Paul M, Leibovici L. Prophylaxis for pneumocystis pneumonia (PCP) in non-HIV immunocompromised patients (Review). Cochrane data of Systematic Reviews 2014, issue 10. DOI: 10.1002/14651858.CD005590.pub3. https://www.ncbi.nlm.nih.gov/pubmed/25269391

 

When should I consider prophylaxis for Pneumocystis pneumonia (PCP) in my patient on prednisone?

My hospitalized patient with pneumonia has now suffered an acute myocardial infarction (MI). Can acute infection and MI be related?

Yes! Ample epidemiological studies implicate infection as an important risk factor for MI.1 The increased risk of MI has been observed during the days, weeks, months or even years following an infection.

A 2018 paper reported a several-fold risk of MI during the week after laboratory-confirmed infection caused by a variety of respiratory pathogens such as influenza virus (6-fold), respiratory syncytial virus (4-fold), and other respiratory viruses (3-fold). 2 Among patients hospitalized for pneumococcal pneumonia, 7-8% may suffer an MI.3,4 One study found a 48-fold increase in the risk of MI during the first 15 days after hospitalization for acute bacterial pneumonia.5 Similarly, an increase in the short-term risk of MI has been observed in patients with urinary tract infection and bacteremia.6

The risk of MI appears to be the highest at the onset of infection and correlates with the severity of illness, with the risk being the highest in patients with pneumonia complicated by sepsis, followed by pneumonia and upper respiratory tract infection. Among patients with pneumonia, the risk exceeds the baseline risk for up to 10 years after the event, particularly with more severe infections.1

Potential mechanisms of MI following infections include release of inflammatory cytokines (eg, interleukins 1, 6, tumor necrosis factor alpha) causing activation of inflammatory cells in atherosclerotic plaques, in turn resulting in destabilization of the plaques. In addition, the thrombogenic state of acute infections, platelet and endothelial dysfunction may increase the risk of coronary thrombosis at sites of plaque disruption beyond clinical resolution of the acute infection. 1

References

  1. Musher DM, Abers MS, Corrales-Medina VF. Acute infection and myocardial infarction. N Engl J Med 2019;380:171-6. https://www.ncbi.nlm.nih.gov/pubmed/30625066
  2. Kwong JC, Schwartz KL, Campitelli MA, et al. Acute myocardial infarction after laboratory-confirmed influenza infection. N Engl J Med 2018;378:345-53. https://www.nejm.org/doi/full/10.1056/NEJMoa1702090
  3. Musher DM, Alexandraki I, Graviss EA, et al. Bacteremic and nonbacteremic pneumococcal pneumonia: a prospective study. Medicine (Baltimore) 2000;79:210-21. https://www.ncbi.nlm.nih.gov/pubmed/10941350
  4. Musher DM, Rueda Am, Kaka As, Mapara SM. The association between pneumococcal pneumonia and acute cardiac events. Clin Infect Dis 2007;45:158-65. https://www.ncbi.nlm.nih.gov/pubmed/17578773
  5. Corrales-Medina VF, Serpa J, Rueda AM, et al. Acute bacterial pneumonia is associated with the occurrence of acute coronary syndromes. Medicine (Baltimore) 2009;88:154-9. https://www.ncbi.nlm.nih.gov/pubmed/19440118
  6. Dalager-Pedersen M, Sogaard M, Schonheyder HC, et al. Risk for myocardial infarction and stroke after community-acquired bacteremia: a 20-year population-based cohort study. Circulation 2014;129:1387-96. https://www.ncbi.nlm.nih.gov/pubmed/24523433

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My hospitalized patient with pneumonia has now suffered an acute myocardial infarction (MI). Can acute infection and MI be related?

My patient with community-acquired pneumonia (CAP) will be going home on an oral antibiotic. Is there a significant difference in the risk of Clostridium difficile infection among the usual CAP antibiotics?

Not all antibiotics are equal in their risk of CDI. Among the common antibiotics used for respiratory tract infections, doxycycline appears to be the least likely to be associated with CDI. 

A population-based case-control study of community-acquired CDI found that while recent exposure increased the risk of CDI for fluoroquinolones, macrolides, cephalosporins, sulfonamides and trimethoprim and penicillins, the risk of CDI with tetracycline use was not increased (1).  Similar findings (with the exception of sulfonamides also appearing risk-neutral) have been reported by others (2). 

Among patients receiving ceftriaxone, receipt of doxycycline has been associated with protection against development of CDI (3).  A 2018 systematic review and meta-analysis also concluded that tetracyclines were associated with a decreased risk of CDI; OR 0.55 (95% CI 0,40-0.75) for doxycycline alone (4). 

 

The most likely explanation for why doxycycline may be associated with lower risk of CDI is its in vitro activity against anaerobes, including C. difficile. Additionally, because of its ability to inhibit protein synthesis, doxycycline may attenuate C. difficile toxin production. Its high bioavailability and maximal absorption from the upper gastrointestinal tract may also mitigate its impact on gut flora, further reducing its risk of CDI (3). 

 

References
1. Delaney JAC, Dial S, Barkun A et al. Antimicrobial drugs and community-acquired Clostridium difficile-associated disease-UK. Emerg Infect Dis 2007:13;761-63. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2738472
2. Kuntz JL, Chirchilles EA, et al. Incidence of and risk factors for community-associated Clostridium difficile infection : A nested case-control study. BMC Infect Dis 2011;11:194. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3154181/ 
3. Doernberg SB, Winston LG, Deck DH, et al. Does doxycycline protect against development of Clostridium difficile infection. Clin Infec Dis 2012;44:615-20. https://www.academia.edu/7814406/Does_Doxycycline_Protect_Against_Development_of_Clostridium_difficile_Infection
4. Tariq R, Cho J, Kapoor S, et al. Low risk of primary Clostridium difficile infection with tetracyclines: a systematic review and metanalysis. Clin Infect Dis 2018; 766:514-27. https://academic.oup.com/cid/article/66/4/514/4161552 

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My patient with community-acquired pneumonia (CAP) will be going home on an oral antibiotic. Is there a significant difference in the risk of Clostridium difficile infection among the usual CAP antibiotics?

My patient with erythema multiforme has tested positive for Mycoplasma pneumoniae IgM antibody. Does this mean she has an acute M. pneumonia infection as the cause of her acute illness?

Not necessarily! Although detection of IgM in the serum of patients has proven valuable in diagnosing many infections during their early phase, particularly before IgG is detected, less well known is that false-positive IgM results are not uncommon. 1

More specific to M. pneumoniae IgM, false-positive results have been reported in 10-80% of patients without a clinical diagnosis of acute M. pneumoniae infection 2-4 and 3-15% of blood donors. 4

False-positive IgM results may also occur when testing for other infectious agents, such as the agent of Lyme disease (Borrelia burgdorferi), arboviruses (eg, Zika virus), and herpes simplex, Epstein-Barr, cytomegalovirus, hepatitis A and measles viruses. 1,5  

Reports of false positive IgM results include a patient with congestive heart failure and mildly elevated liver enzymes who had a false-positive hepatitis IgM which led to unnecessary public health investigation and exclusion from an adult day care center. 1 Another patient with sulfa rash had a false-positive measles IgM antibody resulting in callback of >100 patients and healthcare providers for testing!5

There are many potential mechanisms for false-positive IgM results, including polyclonal B cell activation, “vigorous immune response”, cross-reactive antibodies, autoimmune disease, subclinical reactivation of latent viruses, influenza vaccination, overreading weakly reactive results, and persistence of antibodies long after the resolution of the acute disease. 1,2

In our patient, a significant rise in M. pneumoniae IgG between acute and convalescent samples several weeks apart may be more helpful in diagnosing an acute infection accounting for her erythema multiforme.

 

References

  1. Landry ML. Immunoglobulin M for acute infection: true or false? Clin Vac Immunol 2016;23:540-5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4933779/
  2. Csango PA, Pedersen JE, Hess RD. Comparison of four Mycoplasma pneumoniae IgM-, IgG- and IgA-specific enzyme immunoassays in blood donors and patients. Clin Micro Infect 2004;10:1089-1104. https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(14)63853-2/pdf
  3. Thacker WL, Talkington DF. Analysis of complement fixation and commercial enzyme immunoassays for detection of antibodies to Mycoplasma pneumoniae in human serum. Clin Diag Lab Immunol 2000;7:778-80. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC95955/
  4. Ryuta U, Juri O, Inoue Y, et al. Rapid detection of Mycoplasma pneumoniae IgM antibodies using immunoCard Mycoplasma kit compared with complement fixation (CF) tests and clinical application. European Respiratory Journal 2012; 40: P 2466 (Abstract). https://erj.ersjournals.com/content/40/Suppl_56/P2466 
  5. Woods CR. False-positive results for immunoglobulin M serologic results: explanations and examples. J Ped Infect Dis Soc 2013;2:87-90. https://www.ncbi.nlm.nih.gov/pubmed/26619450

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My patient with erythema multiforme has tested positive for Mycoplasma pneumoniae IgM antibody. Does this mean she has an acute M. pneumonia infection as the cause of her acute illness?