Estimated cumulative incidence of pandemic (H1N1) influenza among pregnant women during the first wave of the 2009 pandemic.
BACKGROUND
Hospitalization and lab confirmed cases of H1N1 have been reported during the first wave of the 2009 pandemic but these are not accurate measures of influenza incidence in the population. We estimated the cumulative incidence of pandemic (H1N1) influenza among pregnant women in the province of Manitoba during the first wave of the 2009 pandemic.


METHODS
Two panels of stored frozen serum specimens collected for routine prenatal screening were randomly selected for testing before (March 2009, n = 252) and after (August 2009, n = 296) the first wave of the pandemic. A standard hemagglutination inhibition assay was used to detect the presence of IgG antibodies against the pandemic (H1N1) 2009 virus. The cumulative incidence of pandemic (H1N1) influenza was calculated as the difference between the point prevalence rates in the first and second panels.


RESULTS
Of the specimens collected in March, 7.1% were positive for the IgG antibodies (serum antibody titre ≥ 1:40). The corresponding prevalence was 15.7% among the specimens collected in August. The difference indicated a cumulative incidence of 8.6% (95% confidence interval [CI] 3.2%-13.7%). The rate differed geographically, the highest being in the northern regions (20.8%, 95% CI 7.9%-31.8%), as compared with 4.0% (95% CI 0.0%-11.9%) in Winnipeg and 8.9% (95% CI 0.0%-18.8%) in the rest of the province.


CONCLUSIONS
We estimated that the cumulative incidence of pandemic (H1N1) influenza among pregnant women in Manitoba during the first wave of the 2009 pandemic was 8.6%. It was 20.8% in the northern regions of the province.
Mahmud
Salaheddin M
SM
Department of Community Health Sciences, University of Manitoba, Winnipeg, Man. salah.mahmud@gmail.com
Becker
Marissa
M
Keynan
Yoav
Y
Elliott
Lawrence
L
Thompson
Laura H
LH
Fowke
Keith
K
Avery
Lisa
L
Van Caeseele
Paul
P
Harlos
Sande
S
Blanchard
James
J
Dawood
Magdy
M
D000293:Adolescent; D000328:Adult; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology; D008350:Manitoba / Q000453:epidemiology; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000453:epidemiology*; D011295:Prenatal Care; D016036:Seroepidemiologic Studies
D007074:Immunoglobulin G
JAMA. 2010 Jan 6;303(1):73-4
20026596
Euro Surveill. 2009 Oct 22;14(42):
19883543
JAMA. 2009 Nov 4;302(17):1872-9
19822627
Br Med Bull. 1979 Jan;35(1):69-75
367490
Dev Biol (Basel). 2003;115:63-73
15088777
BMJ. 2009 Jul 14;339:b2840
19602714
MMWR Morb Mortal Wkly Rep. 2009 May 22;58(19):521-4
19478718
J Obstet Gynaecol Can. 2010 May;32(5):443-447
20500952
Lancet. 2010 Mar 27;375(9720):1100-8
20096450
Obstet Gynecol. 2002 Apr;99(4):531-6
12039105
PLoS Med. 2007 Feb;4(2):e59
17298168