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Don Bandaranayake1, Q. Sue Huang1*, Ange Bissielo1, Tim Wood1, Graham Mackereth2, Michael G. Baker3, Richard Beasley4, Stewart Reid5, Sally Roberts6, Virginia Hope1, on behalf of the 2009 H1N1 serosurvey investigation team?
1 Institute of Environmental Science and Research, National Centre for Biosecurity and Infectious Disease, Upper Hutt, New Zealand, 2 Ministry of Health, Wellington, New Zealand, 3 Wellington School of Medicine, University of Otago, Wellington, New Zealand, 4 Medical Research Institute of New Zealand, Wellington Hospital, Wellington, New Zealand, 5 Ropata Medical Centre, Lower Hutt, New Zealand, 6 Department of Microbiology, Auckland District Health Board, Auckland, New Zealand
Abstract Top
Background
Understanding immunity, incidence and risk factors of the 2009 influenza A(H1N1) pandemic (2009 H1N1) through a national seroprevalence study is necessary for informing public health interventions and disease modelling.
Methods and Findings
We collected 1687 serum samples and individual risk factor data between November-2009 to March-2010, three months after the end of the 2009 H1N1 wave in New Zealand. Participants were randomly sampled from selected general practices countrywide and hospitals in the Auckland region. Baseline immunity was measured from 521 sera collected during 2004 to April-2009. Haemagglutination inhibition (HI) antibody titres of ≥1:40 against 2009 H1N1 were considered seroprotective as well as seropositive. The overall community seroprevalence was 26.7% (CI:22.6?29.4). The seroprevalence varied across age and ethnicity. Children aged 5?19 years had the highest seroprevalence (46.7%;CI:38.3?55.0), a significant increase from the baseline (14%;CI:7.2?20.8). Older adults aged ≥60 had no significant difference in seroprevalence between the serosurvey (24.8%;CI:18.7?30.9) and baseline (22.6%;CI:15.3?30.0). Pacific peoples had the highest seroprevalence (49.5%;CI:35.1?64.0). There was no significant difference in seroprevalence between both primary (29.6%;CI:22.6?36.5) and secondary healthcare workers (25.3%;CI:20.8?29.8) and community participants. No significant regional variation was observed. Multivariate analysis indicated age as the most important risk factor followed by ethnicity. Previous seasonal influenza vaccination was associated with higher HI titres. Approximately 45.2% of seropositive individuals reported no symptoms.
Conclusions
Based on age and ethnicity standardisation to the New Zealand Population, about 29.5% of New Zealanders had antibody titers at a level consistent with immunity to 2009 H1N1. Around 18.3% of New Zealanders were infected with the virus during the first wave including about one child in every three. Older people were protected due to pre-existing immunity. Age was the most important factor associated with infection followed by ethnicity. Healthcare workers did not appear to have an increased risk of infection compared with the general population.
http://www.plosone.org/article/info...onid=DCB5204C58DC9E57C8E484F4C1950124.ambra02
Don Bandaranayake1, Q. Sue Huang1*, Ange Bissielo1, Tim Wood1, Graham Mackereth2, Michael G. Baker3, Richard Beasley4, Stewart Reid5, Sally Roberts6, Virginia Hope1, on behalf of the 2009 H1N1 serosurvey investigation team?
1 Institute of Environmental Science and Research, National Centre for Biosecurity and Infectious Disease, Upper Hutt, New Zealand, 2 Ministry of Health, Wellington, New Zealand, 3 Wellington School of Medicine, University of Otago, Wellington, New Zealand, 4 Medical Research Institute of New Zealand, Wellington Hospital, Wellington, New Zealand, 5 Ropata Medical Centre, Lower Hutt, New Zealand, 6 Department of Microbiology, Auckland District Health Board, Auckland, New Zealand
Abstract Top
Background
Understanding immunity, incidence and risk factors of the 2009 influenza A(H1N1) pandemic (2009 H1N1) through a national seroprevalence study is necessary for informing public health interventions and disease modelling.
Methods and Findings
We collected 1687 serum samples and individual risk factor data between November-2009 to March-2010, three months after the end of the 2009 H1N1 wave in New Zealand. Participants were randomly sampled from selected general practices countrywide and hospitals in the Auckland region. Baseline immunity was measured from 521 sera collected during 2004 to April-2009. Haemagglutination inhibition (HI) antibody titres of ≥1:40 against 2009 H1N1 were considered seroprotective as well as seropositive. The overall community seroprevalence was 26.7% (CI:22.6?29.4). The seroprevalence varied across age and ethnicity. Children aged 5?19 years had the highest seroprevalence (46.7%;CI:38.3?55.0), a significant increase from the baseline (14%;CI:7.2?20.8). Older adults aged ≥60 had no significant difference in seroprevalence between the serosurvey (24.8%;CI:18.7?30.9) and baseline (22.6%;CI:15.3?30.0). Pacific peoples had the highest seroprevalence (49.5%;CI:35.1?64.0). There was no significant difference in seroprevalence between both primary (29.6%;CI:22.6?36.5) and secondary healthcare workers (25.3%;CI:20.8?29.8) and community participants. No significant regional variation was observed. Multivariate analysis indicated age as the most important risk factor followed by ethnicity. Previous seasonal influenza vaccination was associated with higher HI titres. Approximately 45.2% of seropositive individuals reported no symptoms.
Conclusions
Based on age and ethnicity standardisation to the New Zealand Population, about 29.5% of New Zealanders had antibody titers at a level consistent with immunity to 2009 H1N1. Around 18.3% of New Zealanders were infected with the virus during the first wave including about one child in every three. Older people were protected due to pre-existing immunity. Age was the most important factor associated with infection followed by ethnicity. Healthcare workers did not appear to have an increased risk of infection compared with the general population.
http://www.plosone.org/article/info...onid=DCB5204C58DC9E57C8E484F4C1950124.ambra02