Asymptomatic coronavirus disease 2019 (COVID-19) in hospitalized patients

In one week, 7,5% (9 in 120) asymptomatic inpatients were diagnosed with COVID-19 at a hospital with universal face masks policy. Median length of stay was 11 days, suggesting nosocomial infections. Most were presymptomatic with median cycle threshold value of 22, indicating high viral loads.

Notably, 6 patients (66.7%) developed respiratory tract symptoms a median of 2 days (range, 1-5) after the sample collection; thus, they were recategorized as presymptomatic at time of testing, and all required respiratory support: 3 patients (50%) required mechanical ventilation (of these, 2 died and 1 was discharged). The other 3 patients received supplemental oxygen with nasal cannula and 1 of them was discharged. The others are still in the hospital due to their comorbidities. The 3 asymptomatic patients were discharged without complications. The median cycle thresold (Ct) values were 22 (range, 19-37) and 38 (range, 35-39) for the presymptomatic and asymptomatic subgroups, respectively.

Discussion
Most asymptomatic infections were detected in patients who had been in the hospital for longer than the median incubation period for SARS-CoV-2, 2 which suggests nosocomial transmissions.
Considering potential exposure factors, patients 4 and 5 had shared a 2-bed room for at least 72 hours before they received positive test results from samples taken on the same day (Table 1). Notably, they were also among 5 others (patients 2-6) from this cohort who were on the same hospital floor when diagnosed. Despite their allocation to different wards, the same hospital staff circulate through all wards on a daily basis, suggesting a cluster. 2,3 Our findings also suggest the underestimated potential of visitor contribution to viral spread in healthcare facilities. Patient 7 had received visits from his wife, who was asymptomatic and wore a face mask at the time, but a few days afterward developed symptoms and was indeed positive for SARS-CoV-2; therefore, she is retrospectively considered a possible source of exposure. Notwithstanding, patients 7 and 8 had been in the same ward for the previous 9 days and were diagnosed at the same time, regardless of being in different single bedrooms and using protective measures; we considered this to be another possible cluster.
Other factors might have imposed higher risk for these possible nosocomial transmissions. Universal masking may induce a false perception of protection that leads to neglect of other important protective measures, 4 including social distancing and avoiding skin contact. 5 The incorrect use of full protective personal equipment is also concerning, including inadequate hand hygiene 6 or even the incorrect use of masks due to malpositioning, inadequate fabric materials, or inappropriate reuse. Scarce resources also play a part in nosocomial risk of transmission. 7 Nevertheless, asymptomatic individuals, including patients and their visitors, may need to be considered when designing strategies to prevent outbreaks in the healthcare setting, regardless of a universal masking policy.
Finally, previous studies have suggested that only a small fraction of asymptomatic persons may eventually develop symptoms, 1-3,5 but more than half of the initially asymptomatic patients in this study became symptomatic. Perhaps disruption of viral control seen in immunocompromising conditions from the presymptomatic subgroup influenced higher viral loads, 8 demonstrated by the lower Ct values. 9 However, previous reports have suggested similar potential for viral transmission in otherwise healthy, presymptomatic subjects as well, 3,5,10 so it does raise concerns.
The inclusion of healthcare staff and visitors in the screening process could help improve knowledge on viral dynamics in this setting.
In summary, surveillance of asymptomatic COVID-19 in the healthcare setting may be an important measure in reducing nosocomial infections despite universal use of face masks, especially because presymptomatic patients may have high viral loads, suggesting the potential for transmission.