Table 1.
Clinical characteristics of school‐aged children infected with H1N1
| Characteristics | Total no. or mean ± SD (n = 7448) | Cases* no.(%) or mean ± SD (n = 417) | Odds ratio (95% CI) | P value** |
|---|---|---|---|---|
| Age (years) | 12·97 ± 3·03 | 13·24 ± 2·92 | 1·03(1·00–1·07) | 0·42 |
| Primary school | 3139 | 165 (5·3) | ||
| Middle school | 2555 | 144 (5·6) | ||
| High school | 1754 | 108 (6·2) | ||
| Male | 3149 | 225 (7·1) | 1·64 (1·35–2·01) | <0·01 |
| Body mass index (kg/m2) | 19·17 ± 2·77 | 20·13 ± 3·23 | 1·13 (1·10–1·17) | <0·01 |
| <17·25 | 1868 | 75 (4·0) | ||
| 17·25–19·03 | 1831 | 94 (5·1) | ||
| 19·04–20·93 | 1886 | 101 (5·4) | ||
| >20·93 | 1863 | 147 (7·9) | ||
| Waist circumference (cm) | 64·83 ± 7·47 | 68·37 ± 8·54 | 1·08 (1·06–1·10) | <0·01 |
| <60·96 | 1668 | 71 (4·3) | ||
| 60·96–66·03 | 1524 | 72 (4·7) | ||
| 66·04–71·11 | 1972 | 101 (5·1) | ||
| >71·11 | 1867 | 173 (9·3) | ||
| Hand washing | 5·88 ± 3·37 | 5·79 ± 3·58 | 0·99 (0·96–1·02) | 0·58 |
| Wearing a facemask | ||||
| Non‐user | 4164 | 239 (5·7) | 1 (reference) | 0·04 |
| Irregular user | 2819 | 164 (5·8) | 1·02 (0·83–1·25) | |
| Continuous user | 466 | 14 (3·0) | 0·51 (0·30–0·88) | |
| After‐school study hours | 7·91 ± 7·87 | 8·58 ± 7·97 | 1·01 (1·00–1·02) | 0·07 |
| Use of public transportation | 1·84 ± 2·19 | 0·81 ± 0·79 | 0·98 (0·93–1·03) | 0·43 |
| Regular exercise | 2728 | 147 (5·4) | 0·94 (0·76–1·15) | 0·91 |
| Underlying conditions | 1·29 (0·99–1·67) | 0·06 | ||
| Asthma | 171 | 18 (10·5) | ||
| Atopy | 891 | 60 (6·7) | ||
| Cardiac disease | 20 | 2 (10·0) | ||
| Renal disease | 12 | 0 (0·0) | ||
| Liver disease | 11 | 0 (0·0) | ||
| Diabetes | 6 | 0 (0·0) | ||
| Influenza A (H1N1) contact history | 1829 | 216 (11·8) | 3·60 (2·95–4·40) | <0·01 |
| Vaccination | 1719 | 90 (5·2) | 0·92 (0·72–1·17) | 0·49 |
| Overseas trip | 457 (6·1) | 40 (8·8) | 1·68 (1·19–2·36) | <0·01 |
*Influenza A (H1N1) infection was defined as a positive by real‐time RT‐PCR, rapid influenza test, or viral culture result.
Conversely, a negative result by RT‐PCR indicated a lack of influenza A (H1N1) infection. **P values between cases and controls were calculated using the t‐test (for continuous variables), or χ2‐test (for categorical variables). Odds ratios (OR) and 95% confidence intervals (CI) were calculated for each variable for H1N1 infection.
Hand washing frequency was ascertained using a questionnaire with the question, ‘How many times do you wash your hands in a day?’
Facemask use was classified into three groups: nonusers, irregular users (including rare and usual users), or continuous users.
Use of public transportation was defined as time spent riding the bus or subway in a week.
Regular exercise was defined as exercise or physical work for more than 30 min three times a week.
Vaccination was defined as receiving a seasonal vaccination history in 2008 or 2009.
Overseas trip history was defined as having a history of taking a trip abroad in 2009.