Factors associated with transmission
The probability of transmission to household members, detected by NPS,
increased if the index case was an adult compared to a child (62% vs
12%, odds ratio (OR) 12.4, 95% confidence interval (95 Cl) 1.8 to
84.8, p = 0.10), or had a Ct-value below 32 compared to ≥32 (54% vs
21%, OR 4.4, 95 CI 1.1 to 17.1, p = 0.034) (Figure 2A). The probability
of transmission among household members increased by 10% in cases who
were symptomatic, relative to asymptomatic cases (34% vs 44%, OR 1.5,
95 CI 0.7 to 3.4, p = 0.329). Households who employed any
non-pharmaceutical intervention measure were less likely to have
household transmission compared to those without (31% vs 46%, OR 0.5,
95 CI 0.1 to 2.0, p = 0.358), specifically, household separation (27%
vs 45%, OR 0.46, 95 CI 0.1 to 2.2, p = 0.330) and mask wearing (16% vs
43%, OR 0.2, 95 CI 0.0 to 1.6, p = 0.149) were associated with lower
secondary transmission (Figure 2A). Correlation between immune
parameters
SARS-CoV-2 virus detection in saliva positively correlated with evidence
of symptoms (r = 1, p = 0.002) (Figure 2B). Detection of SARS-CoV-2 in
saliva also correlated with SARS-CoV-2 specific plasma IgG (r = 1.0, p
<0.001) and IgM/IgA (r = 1.0, p<0.001) (Figure 2B).
Similarly, detection of SARS-CoV-2 in stool positively correlated with
SARS-CoV-2-specific plasma IgG (r = 1.0, p <0.001) and IgM/IgA
(r = 1.0, p = 0.0015), and showed concordance with detection of
SARS-CoV-2 in saliva (r = 0.83, p<0.001) (Figure 2B). In
SARS-CoV-2 positive children, 72% (13/18) produced Spike 1-specific
salivary antibodies but had no detected serum antibodies (Supplementary
Figure 1).