This is a summary, written by members of the CITF Secretariat, of:

Hohl CM, Cragg A, Purssel E, McAlister FA, Ting DK, Scheuermeyer F, Stachura M, Grant L, Taylor J, Kanu J, Hau JP, Cheng I, Atzema CL, Bola R, Morrison LJ, Landes M, Perry JJ, Rosychuk RJ; Canadian COVID-19 Emergency Department Rapid Response Network (CCEDRRN) investigators for the Network of Canadian Emergency Researchers; Canadian Critical Care Trials Group. Comparing methods to classify admitted patients with SARS-CoV-2 as admitted for COVID-19 versus with incidental SARS-CoV-2: A cohort study. PLoS One. 2023 Sep 26;18(9):e0291580. doi: 10.1371/journal.pone.0291580.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in PLos One, found that among patients admitted to hospital who tested positive for SARS-CoV-2 during the Omicron wave, 52% had a primary diagnosis of COVID-19 and the others had incidental SARS-CoV-2 infections. Patients admitted for COVID-19 were more likely to require intensive care unit (ICU) admission and to die than patients admitted with incidental SARS-CoV-2 infection. Compared to case classification by clinicians, an algorithmCategorizes hospitalizations as being for COVID-19 if the primary discharge diagnosis was COVID-19, or if a patient had a secondary discharge diagnosis of COVID-19 and they were either treated with remdesivir or their primary diagnosis was sepsis, pulmonary embolism, acute respiratory failure, or pneumonia. from the Centers for Disease Control (CDC) was more specific and sensitive but underestimated COVID-19 attributable hospital days, while a Massachusetts classificationCategorizes hospitalizations as being for COVID-19 if the patient received dexamethasone at any time during their hospital visit. had lower sensitivity and specificity, underestimating hospital and ICU bed days and overestimating intubations, ICU admissions, and deaths. The study was led by Dr. Corinne Hohl (University of British Columbia) on behalf of the Canadian COVID-19 Emergency Department Rapid Response Network (CCEDRRN) investigators for the Network of Canadian Emergency Researchers.

Key findings:

  • Of the 42,505 visits by patients to a participating Emergency Department between December 19, 2021, and May 31, 2022, 1,651 patients were admitted and tested positive for SARS-CoV-2, with 858 (52.0%) admitted to hospitalPatients were defined as hospitalized for COVID-19 if they were SARS-CoV-2 positive and hospitalized primarily due to COVID-19 attributable signs and symptoms based on the World Health Organization COVID-19 core case report form, and no plausible alternative diagnosis was made to explain their signs and symptoms. for COVID-19. The others were deemed to have incidental SARS-CoV-2 infectionsHospitalizations in which patients tested SARS-CoV-2 positive, were hospitalized with signs and symptoms other than those attributable to COVID-19 or had an alternative diagnosis that better explained their signs and symptoms or were diagnosed with an exacerbation of a chronic illness that may or may not have been causally related to COVID-19.. Patients hospitalized for COVID-19 required supplemental oxygen more commonly (52.5% vs. 19.7%), spent more days in ICU (median 6.5 vs. 4.0), and had greater in-hospital mortality (12.6% vs. 6.4%) than patients hospitalized with incidental SARS-CoV-2.
  • Using various algorithms, the research team found that ICU admissions were more common among younger patients and death occurred more often among older patients. Patients with a secondary immunodeficiency were more likely to die than those without and patients presenting during the Omicron BA.2 wave were less likely to die than those presenting during the Omicron BA.1 wave. Patients who used illicit substances were more likely to be mechanically ventilated than those who did not.
  • The CDC algorithm had a sensitivity of 82.9% (711/858) for identifying hospitalizations for COVID-19 and a specificity of 98.1% (778/793). Among admissions classified by clinical decision as primarily for COVID-19, the CDC algorithm underestimated intubations by 16.7% (6/36), re-hospitalizations by 18.9% (7/37), ICU hospitalizations by 10.0% (12/120), hospital days by 18.7% (1975/10,584), ICU days by 18.5% (301.5/1629), and in-hospital mortality by 12.0% (13/108). Replacing the clinical definition with the CDC algorithm did not change the statistical significance of the variables.
  • When admissions were classified using the clinical definition or the CDC algorithm, odds of mechanical ventilation, critical care admission, and mortality were all significantly higher among males than females.
  • The Massachusetts classification had a sensitivity of 60.5% (519/858) for identifying COVID-19-related admissions and a specificity of 78.6% (623/793), underestimating the total number of hospital and ICU bed days while overestimating COVID-19-related intubations, ICU admissions, and deaths.
  • The number of hospital and ICU bed days among admissions for COVID-19 were highest among the group classified by clinical decision, followed by the Massachusetts method, and finally, the CDC algorithm.

In this multi-centre study during the Omicron wave, about half of hospitalizations among SARS-CoV-2 positive patients were primarily for COVID-19. These were associated with a greater risk of poor health outcomes and more hospital resource utilization compared to hospitalizations of patients with incidental SARS-CoV-2 infection. Studies that do not differentiate between hospitalization for COVID-19 and incidental SARS-CoV-2 infection when reporting overall mortality rates among hospitalised SARS-CoV-2 patients, are more likely to underestimate virulence in future waves of the pandemic.