Table 2.
Secondary attack rates (SARs) and univariable associations of preventable and non‐preventable risk factors with secondary ILI
| Variable | Category | Household contacts (n = 267) with ILI/total (SAR in %) | OR (95% CI) | P |
|---|---|---|---|---|
| Non‐preventable risk factors | ||||
| Age‐group | 0–4 | 1/17 (5·9) | 0·9 (0·1–8·4) | 0·97 |
| 5–13 | 9/46 (19·6) | 3·7 (1·3–10·8) | 0·02 | |
| 14–34 | 8/56 (14·3) | 2·6 (0·9–7·5) | 0·08 | |
| 35–49 | 7/115 (6·1) | Ref | NA | |
| ≥50 | 2/24 (8·3) | 1·4 (0·3–7·2) | 0·69 | |
| Sex | Female | 14/138 (10·1) | Ref | NA |
| Male | 13/129 (10·1) | 1·0 (0·4–2·2) | 0·99 | |
| Smoker | No | 19/194 (9·8) | Ref | NA |
| Yes | 8/66 (12·1) | 1·3 (0·5–3·1) | 0·59 | |
| Relationship to index patient | Father | 3/73 (4·1) | Ref | NA |
| Mother | 7/83 (8·4) | 2·1 (0·5–8·6) | 0·28 | |
| Sibling | 10/67 (14·9) | 4·1 (1·1–15·6) | 0·04 | |
| Other | 5/38 (13·2) | 3·5 (0·8–15·7) | 0·10 | |
| Vaccination and antiviral therapy | ||||
| Vaccinated against pandemic influenza | No | 26/238 (10·9) | Ref | NA |
| Yes | 1/29 (3·4) | 0·3 (0·04–2·2) | 0·24 | |
| Antiviral therapy of the index patient within 2 days | No | 19/211 (9·0) | Ref | NA |
| Yes | 8/56 (14·3) | 1·7 (0·7–4·1) | 0·25 | |
| Preventable risk factors | ||||
| Close contact* with index patient | 0–1 hours | 6/ 81 (7·4) | Ref | NA |
| 2–4 hours | 10/103 (9·7) | 1·3 (0·5–3·9) | 0·58 | |
| 5–8 hours | 3/51 (5·9) | 0·8 (0·2–3·3) | 0·74 | |
| ≥9 hours | 8/30 (26·7) | 4·5 (1·4–14·5) | 0·01 | |
| Ate meals with index patient** | No | 7/111 (6·3) | Ref | NA |
| Yes | 20/155 (12·9) | 2·2 (0·9–5·4) | 0·09 | |
| Provided care for index patient** | No | 24/230 (10·4) | Ref | NA |
| Yes | 3/37 (8·1) | 0·8 (0·2–2·6) | 0·66 | |
| Slept in the same room regulary *** | No | 20/216 (9·3) | Ref | NA |
| Yes | 7/50 (14·0) | 1·6 (0·6–4·0) | 0·41 | |
| Shared items with index patient regulary*** (towels, clothes) | No | 16/161 (9·9) | Ref | NA |
| Yes | 11/104 (10·6) | 1·1 (0·5–2·4) | 0·87 | |
| Preventive behaviour | ||||
| Cleaned hands more often in general | No | 10/116 (8·6) | Ref | NA |
| Yes | 16/144 (11·1) | 1·3 (0·6–3·0) | 0·51 | |
| Cleaned hands regularly*** | No | 2/19 (10·5) | Ref | NA |
| …after physical contact with index patient | Yes | 1/29 (3·4) | 0·3 (0·03–3·6) | 0·34 |
| Cleaned hands regularly*** | No | 21/202 (10·4) | Ref | NA |
| …after contact with items used by the index patient before | Yes | 5/54 (9·3) | 0·9 (0·3–2·4) | 0·81 |
| Other measures to prevent infection | No | 17/169 (10·1) | Ref | NA |
| Yes | 9/92 (9·8) | 1·0 (0·4–2·3) | 0·94 | |
CI, confidence interval; ILI, influenza‐like illness; OR, odds ratio.
*Close contact: <2 m to index patient.
**More than once per day.
***Regularly: always or mostly.