Abstract
Little is known about the determinants of pandemic H1N1 (pH1N1) infection in Canada among low-income, inner city populations. To inform future influenza planning, the seroprevalence of pH1N1 antibodies among inner city clinic attendees in Winnipeg (Manitoba) according to sociodemographic and risk factor characteristics were estimated and vaccination rates were explored. Adults presenting to three inner city community clinics in Winnipeg from October 2009 to December 2009 were recruited as study participants (n=458). A questionnaire was administered to collect demographic, risk factor and symptom information, and a venous blood sample was collected for hemagglutination inhibition assay testing to detect the presence of antibodies against pH1N1. Approximately one-half (53%) of the study participants reported an annual household income of <$10,000/year, and 65% identified as Aboriginal. pH1N1 positivity was 5.7% among those enrolled early in the study and 15.5% among those enrolled later in the study. Positivity was higher among participants who were female, Aboriginal and in contact with children ≤5 years of age. The overall pH1N1 vaccination rate was 28%. pH1N1 positivity was high among low-income adults accessing clinics in Winnipeg's inner city compared with the general population. Of further concern were the low rates of uptake of both seasonal and pH1N1 influenza vaccinations. When planning for future influenza outbreaks, it is important to incorporate strategies for the prevention, control, and care of influenza among low-income and inner city adults.
Highlights
INTroDuCTIoN: Little is known about the determinants of pandemic H1N1 infection in Canada among low-income, inner city populations
Through the use of questionnaire data and serological testing, we measured the prevalence of pandemic H1N1 (pH1N1) and investigated associations between seropositivity for pH1N1 and socioeconomic, clinical and other putative determinants of pH1N1 infection among adults presenting at three clinics in inner city Winnipeg (Manitoba)
Study population and setting Adults presenting to three inner city community clinics in Winnipeg from October 2009 to December 2009 were recruited as study participants (n=458) using convenience sampling
Summary
Through the use of questionnaire data and serological testing, we measured the prevalence of pH1N1 and investigated associations between seropositivity for pH1N1 and socioeconomic, clinical and other putative determinants of pH1N1 infection among adults presenting at three clinics in inner city Winnipeg (Manitoba). For the first three weeks of participant enrollment, only adults who had not received the pH1N1 vaccine were eligible to participate in the study. The blood specimens were transferred to Cadham Provincial Laboratory (Winnipeg, Manitoba) for hemagglutination inhibition assay (HIA) testing. Laboratory methods The HIA was performed according to standard protocol [8] using the original A/California/04/2009 H1N1 virus strain isolate provided by the Canadian National Microbiology Laboratory (Winnipeg, Manitoba). Data analysis The seroprevalence of pH1N1 antibodies was calculated as the proportion of specimens with HIA titres ≥1:40 [9,10,11] using STATA 9.2 (Stata Corporation, USA). Participants who had received the seasonal or pH1N1 vaccine zero to six days before study enrollment were categorized as unvaccinated, because on average, antibody titres are not detectable by HIA at ≥1:40 until one week after vaccination [13]. Body mass index (BMI) was calculated using height and weight measurements made by the research nurses at the clinics
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