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Volume 19, Number 11—November 2013
Dispatch

Incidence of Influenza A(H1N1)pdm09 Infection, United Kingdom, 2009–2011

Saranya SridharComments to Author , Shaima Begom, Alison Bermingham, Katja Hoschler, Walt Adamson, William Carman, Maria D. Van Kerkhove, and Ajit Lalvani
Author affiliations: Imperial College London, London, UK (S. Sridhar, S. Begom, M.D. Van Kerkhove, A. Lalvani); Public Health England, Colindale, UK (A. Bermingham, K. Hoschler); West of Scotland Specialist Virology Centre, Glasgow, Scotland, UK (W. Adamson, W. Carman)

Main Article

Table 1

Seroprevalence of influenza A(H1N1)pdm09 antibodies at baseline, United Kingdom, 2009–2011*

 Risk factor HI titer, no. (%)†
GMT (95% CI) p value§
<8 8–32 >32 Total p value‡
Total
202 (62.0)
39 (12.0)
85 (26.1)
326

11.6 (10.0–13.4)

Sex
M 92 (58.2) 22 (13.9) 44 (27.8) 158 0.48 12.8 (10.3–15.8) 0.19
F
110 (65.5)
17 (10.1)
41 (24.4)
168

10.6 (8.7–12.8)

Age group, y¶
18–25 57 (44.9) 15 (11.8) 55 (43.3) 127 Ref 20.4 (15.5–26.8) Ref
26–40 99 (73.9) 19 (14.2) 16 (11.9) 134 <0.001 7.8 (6.6–9.1) <0.001
41–55 32 (74.4) 2 (4.7) 9 (20.9) 43 0.01 8.6 (6.2–11.8) <0.001
>56
9 (64.3)
1 (7.1)
4 (28.6)
14
0.29
9.2 (5.3–16.0)
0.14
Seasonal influenza vaccination in 2008#
Yes 23 (54.8) 5 (11.9) 14 (33.3) 42 0.19 12.6 (8.6–18.3) 0.56
No
174 (64.2)
32 (11.8)
65 (24.0)
271

11.1 (9.5–13.0)

Self-reported history of ILI in 3 mo before recruitment**
Yes 9 (36.0) 3 (12.0) 13 (52.0) 25 <0.01 35.7 (16.5–77.0) <0.001
No 189 (64.3) 36 (12.2) 69 (23.5) 294 10.5 (9.2–12.1)

*HI, hemagglutination Inhibition; GMT, geometric mean titer; Ref, referent; ILI, influenza-like illness.
†Of the 342 participants in the study, 16 were missing data on HI assay results.
‡p value comparing the number of persons with a titer >32.
§p value comparing the GMT. For age categories, p value represents the test for trend.
¶Data available for 314 persons.
#Data available for 313 persons.
**Data available for 319 persons.

Main Article

Page created: October 31, 2013
Page updated: October 31, 2013
Page reviewed: October 31, 2013
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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