Secondary infections common in COVID-19, implications unclear


Secondary respiratory infections appear to be highly prevalent among patients with severe COVID-19, but at this point, most pulmonologists aren’t sure what to make of this understudied phenomenon.

Dr. David L. Bowton, professor emeritus, department of anesthesiology, section on critical care, Wake Forest University Baptist Medical Center, Winston Salem, N.C.

Dr. David L. Bowton

“We really do not understand the implications of secondary infections on outcomes in COVID-19 patients,” David L. Bowton, MD, FCCP, said in an interview. “In most early reports the incidence of secondary infections was much higher in patients dying from COVID-19, compared to survivors, but it isn’t clear whether this indicates that the secondary infection itself led to excess mortality or was more a marker of the severity of the COVID-19 infection.

“Further, details of the diagnostic criteria used, the microbiology, and the appropriateness of treatment of these secondary infections has not generally been included in these reports,” added Dr. Bowton, a pulmonologist and professor emeritus of critical care anesthesiology at Wake Forest University, Winston-Salem, N.C.

One such early retrospective cohort study included 191 COVID-19 patients in Wuhan, China. Of the 54 who died in hospital, half had secondary bacterial lung infections (Lancet. 2020 Mar 28;395[10229]:1054-62). That comes as no surprise to U.S. pulmonologists, who learned back in their training that many deaths during the so-called Spanish influenza epidemic of 1918-1920 were actually caused by secondary pneumonia involving Staphylococcus aureus, commented Daniel L. Ouellette, MD, FCCP, associate director of medical critical care at Henry Ford Hospital, Detroit.

Dr. Daniel R. Ouellette

Dr. Daniel R. Ouellette

“Critically ill patients are highly susceptible to secondary infections regardless of the cause of the patient’s critical illness,” he noted in an interview. “Recent reports of secondary infections in patients critically ill from COVID-19 are interesting but should be considered in this context. To confirm that COVID-19 patients have a different, or increased, risk of infection at specific sites or from specific agents will require careful study.”

That will be no easy matter given the challenges of obtaining bronchoalveolar lavage samples in mechanically ventilated patients with COVID-19, according to Eric J. Gartman, MD, FCCP, a pulmonologist at Brown University, Providence, R.I., and director of the pulmonary function laboratory at the Providence Veterans Affairs Medical Center.

“Unfortunately, many of the invasive modalities that are typically employed to help diagnose secondary infections in critically ill patients are being severely limited or even prohibited in COVID-19 patients due to infection control measures,” he said. As a result, Dr. Gartman noted, intensivists are often resorting to empiric broad-spectrum antimicrobial therapy in patients with severe COVID-19 and are without ready access to the bacterial cultures which might otherwise permit later treatment de-escalation or retargeting.

Among the myriad areas of uncertainty regarding COVID-19 is the proportion of bacterial coinfections that are hospital acquired. Given the lengthy duration of invasive mechanical ventilation in patients with severe COVID-19 – a mean of 9.1 days in the United Kingdom – the chances of hospital-acquired infection are likely substantial. Moreover, a recent single-center U.K. study involving microbiologic testing in 195 consecutive patients newly hospitalized for COVID-19 reported that community-acquired bacterial infection was uncommon: Just 4% of patients had pneumococcal coinfection at hospital admission, and S. aureus wasn’t detected in anyone (Lancet. 2020;1:362. doi:10.1016/S2666-5247[20]30036-7). French investigators have reported detecting putative invasive pulmonary aspergillosis in nearly one-third of a small series of 27 consecutive mechanically ventilated COVID-19 patients (Lancet Resp Med. 2020; 8[6]:e48-9). Dr. Gartman said the diagnostic testing methods utilized in this and similar reports haven’t been prospectively validated in COVID-19. The testing methods may not indicate invasive Aspergillus infection in this population with a high degree of certainty, since they have previously been performed mainly in patients with hematologic malignancies.

Dr. Eric J. Gartman,

Dr. Eric J. Gartman

“Although there is nothing definitive regarding this research, as a practicing critical care doctor one should respect these findings and consider this secondary diagnosis if the supporting clinical data is positive, especially given that the mortality risk in this population is high,” he advised.

Dr. Bowton said that he and his fellow intensivists at Wake Forest Baptist Health don’t routinely screen COVID-19 patients for secondary bacterial or fungal infections. And in talking with colleagues around the country, it’s his impression that most have similarly elected not to do so.

“However, our clinical index of suspicion for secondary infections is heightened and, if triggered, will initiate a search for and treatment of these secondary infections,” Dr. Bowton said.

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