Bacterial Pneumonia and Respiratory Culture Utilization among Hospitalized Patients with and without COVID-19 in New York City

COVID-19 is associated with prolonged hospitalization and a high risk of intubation, which raises concern for bacterial co-infection and antimicrobial resistance. Previous research has shown a wide range of bacterial pneumonia rates for COVID-19 patients in a variety of clinical and demographic settings, but none have compared hospitalized COVID-19 patients to patients testing negative for SARS-CoV-2 in similar care settings. We performed a retrospective cohort study on hospitalized patients with COVID-19 testing from 10 March 2020 to 31 December 2020. A total of 19,219 patients were included, of which 3,796 tested positive for SARS-CoV-2. We found a 2.6-fold increase (p < 0.001) in respiratory culture ordering in COVID-19 patients. On a per-patient basis, COVID-19 patients were 1.5-fold more likely than non-COVID patients to have abnormal respiratory cultures (46.8% vs. 30.9%, p < 0.001), which was primarily driven by patients requiring intubation. Among patients with pneumonia, a significantly higher proportion of COVID-19 patients had ventilator-associated pneumonia (VAP) relative to non-COVID patients (85.7% vs 55.1%, p <0.001), but a lower proportion had community-acquired (12.2% vs 22.1%, p < 0.01) or hospital-acquired pneumonia (2.1% vs. 22.8%, p < 0.001). There was also a significantly higher proportion of respiratory cultures positive for MRSA, K. pneumoniae, and antibiotic-resistant organisms in COVID-19 patients. Increased rates of respiratory culture ordering for COVID-19 patients therefore appear to be clinically justified for patients requiring intubation, but further research is needed to understand how SARS-CoV-2 increases the risk of VAP.

Clinical Performance of SARS-CoV-2 Molecular Testing

Molecular testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the gold standard for diagnosis of coronavirus disease 2019 (COVID-19), but the test clinical performance is poorly understood. From 3/10/2020-5/1/2020 NewYork-Presbyterian laboratories performed 27,377 SARS-CoV-2 molecular assays from 22,338 patients. Repeat testing was performed in 3,432 patients, of which 2,413 had negative and 1,019 had positive first day results. Repeat-tested patients were more likely to be older, male, African-American or Hispanic, and to have severe disease. Among the patients with initially negative results, 18.6% became positive upon repeat-testing. Only 58.1% of any-time positive patients had a result of "detected" on the first test. The clinical sensitivity of COVID-19 molecular assays is estimated between 66.2 % and 95.6%, depending on the unknown number of false negative results in single-tested patients. Conversion to a negative result is unlikely to occur before 15 to 20 days after initial testing or 20-30 days after the onset of symptoms, with 50% conversion occurring at 28 days after initial testing. Forty-nine initially-positive patients converted to negative and then back to positive in subsequent days. Conversion from first day negative to positive results increased linearly with each day of testing, reaching 25% probability in 20 days. In summary, our study provides estimates of the clinical performance of SARS-CoV-2 molecular assays and suggests time frames for appropriate repeat testing, namely 15 to 20 days after a positive test and the same or next 2 days after a negative test in a patient with high suspicion for COVID-19.

Bacteremia and Blood Culture Utilization During COVID-19 Surge in New York City

A surge of patients with coronavirus disease 2019 (COVID-19) presenting to New York City hospitals in March 2020 led to a sharp increase in the utilization of blood cultures, which overwhelmed the capacity of automated blood culture instruments. We sought to evaluate the utilization and diagnostic yield of blood cultures during the COVID-19 pandemic to determine prevalence and common etiologies of bacteremia, and to inform a diagnostic approach to relieve blood culture overutilization. We performed a retrospective cohort analysis of 88,201 blood cultures from 28,011 patients at a multicenter network of hospitals within New York City to evaluate order volume, positivity rate, time to positivity, and etiologies of positive cultures in COVID-19. Ordering volume increased by 34.8% in the second half of March 2020 compared to the first half of the month. The rate of bacteremia was significantly lower among COVID-19 patients (3.8%) than COVID-19 negative patients (8.0%) and those not tested (7.1%), p < 0.001. COVID-19 patients had a high proportion of organisms reflective of commensal skin microbiota, reducing the bacteremia rate to 1.6% when excluded. More than 98% of all positive cultures were detected within 4 days of incubation. Bloodstream infections are very rare for COVID-19 patients, which supports the judicious use of blood cultures in the absence of compelling evidence for bacterial coinfection. Clear communication with ordering providers is necessary to prevent overutilization of blood cultures during COVID-19 surges, and laboratories should consider shortening the incubation period from 5 days to 4 days to free additional capacity.