We found that 99.6% of patients without COVID-19 signs or symptoms tested negative for SARS-CoV-2 infection. Of SARS-CoV-2–positive patients, 8 (11.8%) were asymptomatic, corresponding to 0.4% of patients without signs or symptoms of COVID-19. In total, 68 (2.4%) patients tested positive for SARS-CoV-2 infection by PCR. In this prospective multicenter study, hospital staff tested 2,807 patients, of whom 2,278 (81.2%) did not have signs or symptoms of COVID-19. We compared our results with cantonal data (COVID-19 Informationen Schweiz, ). At admission, patients were categorized as asymptomatic, (i.e., absence of all COVID-19 signs or symptoms) or symptomatic (i.e., presence of >1 COVID-19 sign or symptom). When information in the medical chart was inconclusive, we contacted the treating physician or the patient for clarification. Staff extracted these data from the medical records and entered them into an electronic case report form. Before beginning the study, all participating sites agreed to prospectively collect these variables and document them in medical records. Staff also noted whether suspected COVID-19 was the primary reason for admission. The assessment focused on symptoms at the time of the nasopharyngeal sample. In accordance with guidance provided by the Swiss Federal Office for Public Health, staff considered cough, dyspnea, temperature >38.0☌ or feeling feverish, sore throat, and myalgia as possible signs and symptoms of COVID-19 ( 24). Hospital staff assessed each patient for signs and symptoms of COVID-19 at admission. PCR methods varied among the participating study sites ( Appendix Table 1). The laboratory that conducted diagnostic procedures for USZ and GZO also tested and confirmed all SARS-CoV-2–positive samples from patients at STZ and a random subset of SARS-CoV-2–positive samples from patients at KSW. The other 2 hospitals, City Hospital Triemli (STZ) and Cantonal Hospital Winterthur (KSW), sent samples to separate laboratories. A single laboratory conducted diagnostic procedures for the University Hospital of Zurich (USZ) and GZO Wetzikon (GZO). Staff collected a nasopharyngeal swab sample from each patient and tested the samples by PCR. Hospital staff informed admitted patients about SARS-CoV-2 testing as a new routine diagnostic procedure. At the time, the health authorities of the canton supported the policy of universal admission screening. We used the results of this screening to assess SARS-CoV-2 prevalence among hospitalized patients and to evaluate the additional yield of a universal screening strategy compared to a symptom-driven approach.ĭuring the screening period, the hospitals tested all patients >16 years of age for SARS-CoV-2 infection, regardless of signs or symptoms. In the canton of Zurich, Switzerland, 4 hospitals introduced universal admission screening of all hospitalized patients in April 2020. Some well-resourced healthcare settings in high incidence areas might benefit from testing patients without COVID-19 symptoms ( 22). For example, some hospitals might screen patients for SARS-CoV-2 infection within 24 hours before an elective intervention ( 21). In consideration of these circumstances, hospitals must take precautions to prevent the spread of SARS-CoV-2. Many hospitalized patients, who frequently are >65 years of age, have concurrent conditions, or both, are at risk for severe COVID-19. Asymptomatic persons and healthcare workers can contract and spread the infection among hospitalized patients. In many healthcare settings, the number of persons with asymptomatic SARS-CoV-2 infection is unknown. published evidence of asymptomatic SARS-CoV-2 transmission ( 18), and evidence that asymptomatic or presymptomatic persons can transmit SARS-CoV-2 infection has continued to increase ( 19, 20). A high proportion of hospitalized COVID-19 patients have concurrent conditions such as arterial hypertension, diabetes mellitus, or coronary heart disease ( 13– 17). Common signs and symptoms of COVID-19 include fever, cough, sputum production, and fatigue ( 11, 12). COVID-19 has many manifestations, ranging from mild upper airway symptoms to acute respiratory distress syndrome. Among symptomatic patients, men are affected slightly more frequently than women ( 9, 10). The median incubation period is ✵ days ( 7, 8). The transmission mode of SARS-CoV-2 is not fully understood it is thought to be spread mostly by respiratory droplets and direct contact ( 4– 6). The World Health Organization declared a pandemic on Ma( 1– 3), in response to the rapid international spread of COVID-19. In early 2020, public health officials identified the illness as coronavirus disease (COVID-19) and its causative agent as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In late 2019, a pneumonia of unknown etiology emerged in Wuhan, Hubei Province, China.
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