Discussion

Voluntary mass testing of asymptomatic HCP at our healthcare system revealed a very low period-prevalence rate of SARS-CoV-2 when community transmission was high and state-wide test positivity rates exceeded 5% for nearly half our study period. HCP prevalence was substantially lower than concurrent rates seen in our community, supporting the effectiveness of protective measures such as personal protective equipment, which included universal face mask use, and respirators with eye protection for all COVID-19 care, and adherence to public health recommendations. HCP were enthusiastic to be tested and over a third of our workforce enrolled.

Interestingly, half of positive HCP reported mild symptomatology after being informed of their positive results, including isolated headaches, fatigue, and nasal congestion. This finding suggests a broad spectrum of symptom severity and type that raise concern subclinical symptoms may be missed or minimized, especially in exposure investigation. Mild symptoms do not exclude a diagnosis of COVID-19, and such guidance should be incorporated in HCP staffing policies. One prior study noted substantial variation in the initial reported symptom(s) from HCP consistent with our data,^{Reference Malenfant, Newhouse and Kuo3} and another showed nearly half of HCP did not suspect prior COVID-19 after positive serology.^{Reference Self, Tenforde and Stubblefield4} Although symptom screening is insensitive, it may, in conjunction with sufficient testing, increase the sense of safety by HCP.

Given our low positivity rates, the utility of mass asymptomatic testing remains uncertain. Asymptomatic mass testing in high-risk congregate living environments (eg, college campuses and skilled nursing facilities) may help identify and limit COVID-19 spread, but the value of such mass testing in healthcare settings, where resources are limited and appropriate infection prevention practices better mitigate transmission, is less clear. Several modeling studies now support mass testing in healthcare settings to prevent asymptomatic spread.^{Reference Black, Bailey, Przewrocka, Dijkstra and Swanton5,Reference Chin, Huynh, Chapman, Murrill, Basu and Lo6} Our experience suggests there could be substantial benefit in encouraging testing of staff with any degree of symptoms, even mild because up to half of positive HCP would be detected by this strategy.

This study has several limitations. We were unaware of an individual’s exposures or previous infection. Selection bias may have occurred as a result of convenience sampling and symptom underreporting. Recall bias may have occurred with positive staff. We were unable to distinguish true from false positives with confirmatory testing. The anticipated specificity of the Aptima SARS-CoV-2 assay is extremely high, but in a low disease-prevalence setting (1%), even a specificity of 99% would be associated with a false-positive rate of 50%. A substantial fraction of our 15 asymptomatic cases may have been false positives. However, we would still anticipate being able to detect all true asymptomatic positives through mass testing.^{Reference Skittrall, Wilson and Smielewska7,Reference Zhen, Manji, Smith and Berry8} Lastly, NAAT is contingent on viral dynamics and serology may identify additional prior SARS-CoV-2 infections in HCP.