Are presymptomatic SARS-CoV-2 infections in nursing home residents unrecognised symptomatic infections? Sequence and metadata from weekly testing in an extensive nursing home outbreak

Abstract

Background: Sars-CoV-2 outbreaks resulted in a high case fatality rate in nursing homes (NH) worldwide. It is unknown to which extent presymptomatic residents and staff contribute to the spread of the virus.

Aims: To assess the contribution of asymptomatic and presymptomatic residents and staff in SARS-CoV-2 transmission during a large outbreak in a Dutch NH.

Methods: Observational study in a 185-bed NH with two consecutive testing strategies: testing of symptomatic cases only, followed by weekly facility-wide testing of staff and residents regardless of symptoms. Nasopharyngeal and oropharyngeal testing with RT-PCR for SARs-CoV-2, including sequencing of positive samples, was conducted with a standardised symptom assessment.

Results: 185 residents and 244 staff participated. Sequencing identified one cluster. In the symptom-based test strategy period, 3/39 residents were presymptomatic versus 38/74 residents in the period of weekly facility-wide testing (P-value < 0.001). In total, 51/59 (91.1%) of SARS-CoV-2 positive staff was symptomatic, with no difference between both testing strategies (P-value 0.763). Loss of smell and taste, sore throat, headache or myalga was hardly reported in residents compared to staff (P-value <0.001). Median Ct-value of presymptomatic residents was 21.3, which did not differ from symptomatic (20.8) or asymptomatic (20.5) residents (P-value 0.624).

Conclusions: Symptoms in residents and staff are insufficiently recognised, reported or attributed to a possible SARS-CoV-2 infection. However, residents without (recognised) symptoms showed the same potential for viral shedding as residents with symptoms. Weekly testing was an effective strategy for early identification of SARS-Cov-2 cases, resulting in fast mitigation of the outbreak.

Keywords: COVID-19; nursing home; older people; presymptomatic; residents; staff.

Figure 1

COVID-19 by date of onset and NH policy, shows the date of onset of COVID-19 for participating residents of the different wards and participating staff from the 15th of April until the 2nd of June. Key changes in NH policy for infection prevention and testing are indicated. On May 13th, facility management decided to move all positive tested residents to the first floor of the building, while residents who tested negative were moved to the ground floor of the building. PPE used on the first floor included isolation gown, gloves over the wrists, goggles and a surgical mask; on the ground floor surgical masks and gloves were used.

Figure 2

Zoom-in of Dutch phylogenetic tree, with sequences of NH A in red (clients) and orange (employees). Sequences in blue originate from the related hospital outbreak. Sequences in black originate from a Dutch national reference database.

Figure 3

Frequency plot of days until development of symptoms from positive PCR-test of residents. Negative values represent symptomatic residents, while positive values represent presymptomatic residents. The value 0 means that residents developed symptoms at the day of PCR-test: whether the symptoms developed before or after testing determines if they were presymptomatic or symptomatic. (A) symptomatic testing strategy until the 11th of May. (B) Addition of facility-wide weekly testing strategy regardless of symptoms from the 12th of May.