Note: The risk of bias by domain corresponds to the highest risk of bias among outcomes by domain.
The overall risk of bias corresponds to the overall highest risk of bias assessed among outcomes.
| Bias | Author's judgement | Support for judgement |
| Confounding |
Serious |
The analysis appears to account only for age group (adult/teenager vs child), so did not adjust well for our prespecified confounding factors. Uncontrolled confounding is likely. |
| Selection of participants into the study |
Low |
No particular concerns in this domain. |
| Clasification of interventions |
Serious |
Information to classify the intervention groups was recorded retrospectively by self report. |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Low |
No particular concerns in this domain - data were reasonably complete. |
| Measurement of the outcome |
Low |
No particular concerns in the domain - PCR test performed at day one and ten days after exposure. |
| Selection of the reported results |
Moderate |
There is no evidence of a protocol/analysis plan, and we have concerns that results could have been selected for reporting because of the findings. |
| Overall risk of bias |
Serious |
|
| Overall comment | Concerns regarding residual confounding (age, sex, comorbidities, socioeconomic status and ethnicity were not considered) and about information used to classify the intervention groups recorded retrospectively by self report. |