Pregnancy as a risk factor for severe influenza infection: an individual participant data meta-analysis

Background: WHO identifies pregnant women to be at increased risk for severe outcomes from influenza virus infections and recommends that they be prioritized for influenza vaccination. The evidence supporting this, however, is inconsistent. Ecologic studies in particular suggest more severe outcomes from influenza infection during pregnancy than studies based on individual patient data. Individual studies however may be underpowered and, as reported in a previous systematic review, confounding factors could not be adjusted for. We therefore conducted an individual participant data meta-analysis to assess the risk for severe outcomes of influenza infection in pregnant women while adjusting for other prognostic factors. Methods: We contacted authors of studies included in a recently published systematic review. We pooled the individual participant data of women of reproductive age and laboratory confirmation of influenza virus infection. We used a generalized linear mixed model and reported odds ratios (OR) and 95% confidence intervals (CI). Results: A total of 33 datasets with data on 186,656 individuals were available, including 36,498 eligible women of reproductive age and known pregnancy status. In the multivariable model, pregnancy was associated with a 7 times higher risk of hospital admission (OR 6.80, 95%CI 6.02–7.68), among patients receiving medical care as in- or outpatients, pregnancy was associated with a lower risk of admission to intensive care units (ICU; OR 0.57, 95%CI 0.48–0.69), and was not significantly associated with death (OR 1.00, 95%CI 0.75–1.34). Conclusions: Our study found a higher risk of influenza associated hospitalization among pregnant women as compared to non-pregnant women. We did not find a higher mortality rate or higher likelihood of ICU admission among pregnant women who sought medical care. However, this study did not address whether a true community based cohort of pregnant women is at higher risk of influenza associated complications.Fil: Mertz, Dominik. Mc Master University; CanadáFil: Lo, Calvin Ka Fung. Mc Master University; CanadáFil: Lytvyn, Lyubov. Mc Master University; CanadáFil: Ortiz, Justin R.. Organizacion Mundial de la Salud; ArgentinaFil: Loeb, Mark. Mc Master University; CanadáFil: Ang, Li Wei. Ministry of Health; SingapurFil: Anlikumar, Mehta Asmita. Amrita Vishwa Vidyapeetham; IndiaFil: Bonmarin, Isabelle. Santé publique; FranciaFil: Borja Aburto, Victor Hugo. Instituto Mexicano del Seguro Social; MéxicoFil: Burgmann, Heinz. Medical University Vienna; AustriaFil: Carratalà, Jordi. Universidad de Barcelona; España. Instituto de Investigación Biomédica de Bellvitge; España. Spanish Network for Research in Infectious Diseases; EspañaFil: Chowell, Gerardo. Georgia State University; Estados Unidos. National Institutes of Health; Estados UnidosFil: Cilloniz, Catia. Universidad de Barcelona; España. Instituto de Investigaciones Biomédicas August Pi i Sunyer; EspañaFil: Cohen, Jessica. Centers for Disease Control and Prevention; Estados UnidosFil: Cutter, Jeffery. Ministry of Health; SingapurFil: Filleul, Laurent. Santé publique; Francia. French National Public Health Agency; FranciaFil: Garg, Shikha. Centers for Disease Control and Prevention; Estados UnidosFil: Geis, Steffen. London School of Hygiene and Tropical Medicine; Reino UnidoFil: Helferty, Melissa. Public Health Agency; CanadáFil: Huang, Wan Ting. Taiwan Centers for Disease Control; ChinaFil: Jain, Seema. Centers for Disease Control and Prevention; Estados UnidosFil: Sevic, Biljana Joves. Institute for Pulmonary Diseases of Vojvodina; SerbiaFil: Kelly, Paul. Australian Capital Territory Health Directorate; Australia. Australian National University Medical School; AustraliaFil: Kusznierz, Gabriela. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorios e Instituto de Salud "Dr. C. G. Malbran". Instituto Nacional de Enfermedades Respiratorias; ArgentinaFil: Lehners, Nicola. Ruprecht Karls Universitat Heidelberg; AlemaniaFil: Lenzi, Luana. Universidade Federal do Paraná; BrasilFil: Ling, Ivan T.. Sir Charles Gairdner Hospital; AustraliaFil: Mitchell, Robyn. Public Health Agency; CanadáFil: Mulrennan, Siobhain A.. Sir Charles Gairdner Hospital; Canadá. University of Western Australia; AustraliaFil: Nishioka, Sergio A.. Ministerio de Salud de Brasil; BrasilFil: Norton, Robert. Townsville Hospital; AustraliaFil: Oh, Won Sup. Kangwon National University School of Medicine; Corea del SurFil: Orellano, Pablo Wenceslao. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin