Influenza-like illness among pregnant Chinese women in Hong Kong

The World Health Organization recently recommended pregnant women as the highest priority group for the seasonal influenza vaccination. It is therefore crucial to monitor its progress by assessing the burden of influenza. The prevalence of influenza among pregnant women and its associated maternal outcomes have rarely been addressed and increasing evidence suggests that their burden of influenza is affected by the underlying medical conditions. This study recruited 2670 new mothers during the summer of 2011 and used a validated questionnaire to assess the demographic background, underlying chronic illnesses, respiratory symptoms during pregnancy and pregnancy outcomes. Multivariate logistic regression was used to explore (1) the association between pre-existing chronic illnesses and the risk of ILI/ARI and (2) the link between ILI/ARI and adverse maternal outcomes. The prevalence of ILI and ARI was 11.5% and 34.9% during the 2011 influenza season. Only 1.8% of participants had received seasonal influenza vaccine during pregnancy and 4% had pre-existing chronic illnesses. Both chronic and respiratory illnesses were significantly associated with the risk of ARI but not ILI. There was no association between ILI/ ARI and adverse maternal outcomes. This is one of a few studies reporting the prevalence of ILI among pregnant women which is essential, as a baseline, to monitor the benefits of the future influenza program. Our study showed no significant association between existing chronic illnesses among pregnant women and their risk of ILI, suggesting that pregnancy is an independent risk factor for influenza and is not strongly affected by underlying chronic illnesses.