Cowling 2009.
| Methods | Cluster‐randomised controlled trial | |
| Participants | Households in Hong Kong From 45 outpatient clinics in both the private and public sectors across Hong Kong, they enrolled persons who reported at least 2 symptoms of acute respiratory illness (temperature 37.8 °C, cough, headache, sore throat, or myalgia); had symptom onset within 48 hours; and lived in a household with at least 2 other people, none of whom had reported acute respiratory illness in the preceding 14 days. After participants gave informed consent, they provided nasal and throat swab specimens. 2750 patients were eligible and tested between 2 January through 30 September 2008. Included were 407 people with influenza‐like illness who were positive for influenza A or B virus by rapid testing (index patients) and 794 household members (contacts) in 331 households |
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| Interventions | Participants with a positive rapid test result and their household contacts were randomly assigned to 1 of 3 study groups: control (lifestyle measures ‐ 134 households), control plus enhanced hand hygiene only (136 households) and control plus face masks and enhanced hand hygiene (137 households) for all household members. No detailed description of the instructions given to participants | |
| Outcomes | Influenza virus infection in household contacts, as confirmed by reverse transcription polymerase chain reaction (RT‐PCR) or diagnosed clinically after 7 days "The primary outcome measure was the secondary attack ratio at the individual level: that is, the proportion of household contacts infected with influenza virus. We evaluated the secondary attack ratio using a laboratory definition (a household contact with a nose and throat swab specimen positive for influenza by RT‐PCR) as the primary analysis and 2 secondary clinical definitions of influenza based on self‐reported data from the symptom diaries as secondary analyses." Statistical analysis: adjusted for clustering Results: no significant difference in secondary attack ratio between groups in total population. Statistically significant reduction in RT‐PCR confirmed influenza virus infections in the household contacts in 154 households in which the intervention was applied within 36 hours of symptom onset in the index patient. Adherence to hand hygiene between 44% and 62%. Adherence of index patient to wearing a face mask between 15% and 49% |
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| Notes | "In an unintentional deviation from that protocol, 49 of the 407 randomly allocated persons had a household contact with influenza symptoms at recruitment (a potential co‐index patient). We also randomly assigned 6 of 407 persons who had symptoms for slightly more than 48 hours." The authors conclude that "Hand hygiene and face masks seemed to prevent household transmission of influenza virus when implemented within 36 hours of index patient symptom onset. These findings suggest that non‐pharmaceutical interventions are important for mitigation of pandemic and interpandemic influenza. " |
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| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | Randomisation was computer‐generated by a biostatistician "A pre‐specified table of random numbers will be used to assign one of the three interventions to the household of the index case." |
| Allocation concealment (selection bias) | Low risk | The households of eligible study index patients were allocated to 3 groups in a 1:1:1 ratio under a block randomisation structure with randomly permuted block sizes of 18, 24 and 30 by using a random‐number generator. Allocation was concealed from treating physicians and clinics and implemented by study nurses at the time of the initial household visit |
| Blinding (performance bias and detection bias) All outcomes | High risk | Participants and people who administered the interventions were not blinded to the interventions, but participants were not informed of the specific nature of the interventions applied to other participating households |
| Incomplete outcome data (attrition bias) All outcomes | High risk | Dropout was accounted for. Dropout from randomised population was high: 32% in control group, 37.5% in hand hygiene group and 39.4% in the face masks and hand hygiene group. Reasons for dropout distributed evenly over the 3 groups Authors report follow up as proportion of patients remaining in the study after initial dropout |
| Selective reporting (reporting bias) | Unclear risk | In general good reporting |