Despite frequent use of empiric antibiotics in hospitalized patients with Covid-19,¹  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%). ² 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.⁷  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. ¹  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/

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