Clinical samples were almost comprised of nasopharyngeal and oropharyngeal swabs (95.75%), and also tracheal aspirate (2.05%), stool (1.67%), and other fluids (0.53%).
We excluded the entry of more than two samples from the same individual per month to avoid bias on the frequency rates. Hence, 8,644 were included in the analysis (5,241 samples from HP, and 3,403 from HCW).
From March 2020 to April 2021, we performed a mean of 617.43 ± 187.05 COVID-19 diagnostics per month (374.36 ± 93.73 for HP, and 243.07 ± 128.44 for HCW). The overall SARS-CoV-2 frequency rate was 31.27% (2703/8644). In HP and HCW, the frequency rates were 32.23% (1689/5241), and 29.80% (1014/3403), respectively, which have significantly differed (p = 0.0173). The frequency rates of HP and HCW by month per year, and their statistical differences, are shown in Table 1.
Higher frequency rates of positive samples in HP were detected in adults aging 50-59 years (42.11%), and elderly over 60 years old (43.03%), with a significant difference from those of HCW (30.64%, p < 0.0001; and 30.51%, p = 0.0076, respectively) for the same age groups. On the other hand, in HCW, the frequency rates have not differed statistically within age groups.
The epidemic curves of COVID-19 observed at Hospital Sao Paulo for HP and HCW were comparable most of the time during the course of disease over time (Figure 1), although the SARS-CoV-2 frequency rates in HP were significantly higher than HCW in April, May, and December 2020, and January, March and April 2021, and the opposite in June 2020 (Table 1).
During the first SARS-CoV-2 wave, from March to October 2020, the positivity in HP and HCW reached their peaks in April (51.6%) and June (51.2%), respectively, whereas the lowest frequency rates were observed in October for both groups, with 13.9% for HP and 11.00% for HCW (Table1, Figure 1). The frequency rates started to increase again in November 2020, reaching a new peak in January 2021, when HCW started to be immunized in Brazil.
In December 2020, January and April 2021, frequency rates of SARS-CoV-2 were significantly higher in HP in relation to HCW (p = 0.0007, p < 0.0001, p = 0.0176, respectively). Interestingly, frequency rates in HCW were almost the same during the first three months of 2021 (24.31%, 22.86%, and 22.12%, respectively) and dropped to 14.06% in April. In 2021, for HP, the frequency rate oscillated in February (25.56%), and March (34.39%), and dropped in April (22.48%).
In March 2021 we tested the highest number of HP samples since the beginning of the COVID-19 pandemic when VOC P.1 was first confirmed at Hospital São Paulo in more than 84% of all sequenced samples [9].
The age of HP ranged from 0 to 101 years, with a mean of 47.28 ± 24.56 years, and a median of 52 years. On the HP positive for SARS-CoV-2, the age range was the same, with a mean of 57.26 ± 18.29 years, and a median of 59 years (range 55-66) over the analyzed period. There was a significant difference (p = 0.0023) between the months with the lowest (52.75 ± 20.18) and highest (62.99 ± 18.62) mean ages, which corresponded to November and December 2020, respectively (Figure 2). There was no significant difference in the mean ages since the predominance of VOC P.1 on March 2021.
For HCW, the age varied from 14 to 92 years (mean = 37.24 ± 11.4; median = 36), and in the SARS-CoV-2 positives, the age varied from 19 to 78 years (mean = 37.58 ± 11.49; median = 36), with no statistical differences within the mean age over the time.
The RT-qPCR Ct values, computed from July 2020 to April 2021, ranged from 9 to 40 (mean = 25.55 ± 6.07; median = 25) for HP, and 10 to 40 (mean = 23.68 ± 5.82; median = 23) for HCW, with a significant difference between the groups (p = 0.0023). The mean Ct values have not statistically differed within HP and HCW groups over time, even since the beginning of HCW vaccination or VOC P.1 predominance (Figure 3).