Volume 19, Number 11—November 2013
Dispatch
Incidence of Influenza A(H1N1)pdm09 Infection, United Kingdom, 2009–2011
Saranya Sridhar
, Shaima Begom, Alison Bermingham, Katja Hoschler, Walt Adamson, William Carman, Maria D. Van Kerkhove, and Ajit Lalvani
, Shaima Begom, Alison Bermingham, Katja Hoschler, Walt Adamson, William Carman, Maria D. Van Kerkhove, and Ajit Lalvani
Table 2
Risk factors for natural infection with influenza A(H1N1)pdm09, United Kingdom*
| Risk factor | Second pandemic wave (Sep 2009–Apr 2010) |
Third pandemic wave (Aug 2010–Apr 2011) |
||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Infection status, no.(%) |
Unadjusted |
Adjusted† |
Infection status, no. (%) |
Unadjusted |
Adjusted† |
|||||||||||||
| None | Natural‡ | Total | OR (95% CI) | p value | OR (95% CI) | p value | None | Natural‡ | Total | OR (95% CI) | p value | OR (95% CI) | p value | |||||
| Total | 210 (86.4) | 26 (10.7) | 242 | 119 (80.4) | 28 (19.6) | 148 | ||||||||||||
| Sex | ||||||||||||||||||
| M | 95 (87.2) | 14 (12.8) | Ref | 53 (85.5) | 9 (14.5) | 62 | Ref | |||||||||||
| F | 121 (91.9) | 12 (9.0) | 0.67 (0.30–1.52) | 0.34 | 0.68 (0.30–1.58) | 0.37 | 66 (76.7) | 20 (23.3) | 86 | 1.78 (0.75–4.24) | 0.19 | 1.67 (0.69–4.26) | 0.28 | |||||
| Age group, y | 0.99 (0.95–1.03) | 0.6 | 0.98 (0.93–1.02) | 0.29 | ||||||||||||||
| 18-25 | 75 (91.5) | 7 (8.5) | 82 | Ref | Ref | 33 (80.5) | 8 (19.5) | 41 | Ref | |||||||||
| 26-40 | 98 (89.1) | 12 (10.9) | 110 | 1.31 (0.49–3.49) | 0.59 | 53 (74.7) | 18 (25.4) | 71 | 1.40 (0.55–3.58) | 0.48 | ||||||||
| 41-55 | 30 (85.7) | 5 (14.3) | 35 | 1.79 (0.53–6.07) | 0.35 | 23 (88.5) | 3 (11.5) | 26 | 0.54 (0.13–2.25) | 0.39 | ||||||||
| >56 | 10 (90.9) | 1 (9.1) | 11 | 1.07 (0.12–9.64) | 0.95 | 7 (57.1) | 0 | 7 | – | – | ||||||||
| Not known | 4 (80.0) | 1 (20.0) | 5 | 3 (100.0) | 0 | |||||||||||||
| Titer at start of season | 0.98 (0.97–1.01) | 0.23 | 0.92 (0.86–0.99) | 0.04 | ||||||||||||||
| <8 | 140 (88.5) | 18 (11.5) | 158 | Ref | Ref | 61 (70.1) | 26 (29.9) | 87 | Ref | |||||||||
| 8–32 | 49 (89.1) | 6 (10.9) | 55 | 0.95 (0.36–2.54) | 0.92 | 23 (88.5) | 3 (11.5) | 26 | 0.31 (0.08–1.11) | 0.07 | ||||||||
| >32 | 27 (93.1) | 2 (6.9) | 29 | 0.58 (0.13–2.63) | 0.48 | 35 (100) | 0 | 35 | – | – | ||||||||
*Ref, referent; –, cannot be calculated.
†Adjusted for the other covariates. In the logistic regression undertaken the dependent variable was infection status and age, sex and titer at the start of the season were the independent variables. The results shown are from a single run, and no other model was fitted. Hosmer Lemeshow goodness-of-fit statistic showed an adequate fit for the logistic regression models fitted to the second wave and the third wave data (Hosmer Lemeshow statistic was 4.69 ,p = 0.58 for the second wave and 5.54, p = 0.59 for the third wave).
‡Natural infection indicates incident infection among those susceptible at the beginning of the wave.
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