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, ^{Reference Al-Sadeq and Nasrallah2} 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. ^{Reference Al-Sadeq and Nasrallah2,Reference Arons, Hatfield and Reddy3}

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, ^{Reference Howard, Huang, Li, Tufekci, Zdimal and van der Westhuizen4} including social distancing and avoiding skin contact. ^{Reference Hijnen, Marzano and Eyerich5} 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. ^{Reference Dato, Hostler and Hahn7}

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, ^{Reference Oran and Topol1–Reference Arons, Hatfield and Reddy3,Reference Hijnen, Marzano and Eyerich5} 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, ^{Reference Uematsu, Sakai and Kihira8} demonstrated by the lower Ct values. ^{Reference Bullard, Dust and Funk9} However, previous reports have suggested similar potential for viral transmission in otherwise healthy, presymptomatic subjects as well, ^{Reference Arons, Hatfield and Reddy3,Reference Hijnen, Marzano and Eyerich5,Reference Huang, Wang, Li, Ren, Zhao and Hu10} 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.