Low Clinical Burden of 2009 Pandemic Influenza A (H1N1) Infection during Pregnancy on the Island of La Réunion

Patrick Gérardin,Philippe Guillermin,Georges Barau,Hanitra Randrianaivo,Arnaud Winer,Rachid El Amrani,Alain Michault,Malik Boukerrou,Marie-Christine Jaffar-Bandjee,Jean-Fabien Rouanet,Béatrice Cyrille,Brahim Boumahni,Pierre-Yves Robillard,Marc Gabrièle,Michel Bohrer,Adam J Ratner

doi:10.1371/journal.pone.0010896

Abstract

BackgroundPregnant women have been identified as a group at risk, both for respiratory complications than for the admissions to the Intensive Care Unit (ICU) during the 2009 H1N1 influenza pandemic (pdm). The purpose of this prospective register-based cohort-study was to characterize the clinical virulence of the pdm (H1N1/09)v during pregnancy in La Réunion.Methods/Principal FindingsOver a twelve-week pdm wave (13 July to 3 October 2009), 294 pregnant women presented with an influenza-like illness (ILI) to one of the three maternity departments of the South Reunion area, Indian Ocean. Out of these, 278 were checked by RT-PCR for influenza viruses (157 positive and 121 negative, of whom, 141 with pdm flu and 132 with ILIs of non pdm origin, 5 untyped). The median body temperature was higher in women experiencing pdm flu than in those with non pdm ILI (38.9°C versus 38.3°C, P<0.0001), without evidence linked to circulating viremia. Oseltamivir was given for 86% of pdm flu cases in a median time inferior than 48 hrs (range 0–7 days). The hospitalization rate for pdm flu was of 60% and not associated with underlying conditions. Six viral pneumonia and fourteen asthma attacks were observed among 84 hospitalized pdm flu cases, of whom, only one led to the ICU for an acute lung injury. No maternal death occurred during the pdm wave. None adverse pregnancy outcome was associated with pdm flu. No congenital birth defect, nor early-onset neonatal influenza infection was attributable to pdm flu exposure.Conclusions/SignificanceThis report mitigates substantially the presumed severity of pandemic H1N1/09 influenza infection during pregnancy. The reasons for which the clinical burden of H1N1/09 influenza virus may differ worldwide raise questions about a differential local viral-strain effect and public health preparedness, notably in timely access to special care and antiviral treatments.

Highlights

During the twelve-wk of the pdm wave in La Reunion, which lasted for pregnant women from July 13 to October 3, out of 4,100 estimated ongoing pregnancies, 294 (7%) pregnant women were referred to a flu-dedicated consultation in one of the three South Reunion maternity departments, representing nearly half of the obstetrical visits during that period (45%, 294/653 passages)
During the twelve-wk pdm wave, only two neonates were referred late in neonatal care unit for mild symptoms, due to household transmission. This hospitalized-based cohort, designed from a well-tested regional representative birth register [25], identified all pregnant women referred to the South Reunion Island maternities for influenza-like illness (ILI) or any complaint compatible with flu throughout the 2009 pdm influenza wave, which occurred in La Reunion, between July 13 and October 3, during the austral winter season
Our findings, acquired without major selection bias nor critical strain on the healthcare supply, mitigate historical and recent disturbing data on severe pdm influenza in pregnant women highlighting increased risks for hospitalization or admission to the Intensive Care Unit (ICU) [4,6,13,14,15,16,17,18,19,20,21]. This current overview provides some arguments to demonstrate the low clinical virulence of pdm influenza (H1N1/09)v, in a context of a public health response focused on the prompt identification of clinical cases and managing clusters of infections with widespread use of antiinfluenza drugs

Summary

Introduction

Since the beginning of the first third-millennium pandemic, foremost was the concern that 2009 triple-reassortant pandemic (pdm) H1N1 influenza (H1N1/09) virus could be more lifethreatening than its seasonal peers [1], as evidenced by its unusual clinical burden in young adults [2,3,4,5,6], who experienced more than half of Intensive Care Unit (ICU) stays and deaths [6,7,8,9], mainly due to the acute respiratory distress syndrome (ARDS) complicating pneumonia of viral origin [4,7,8,9] In this context suggesting enhanced virulence for this novel influenza strain, further supported by alveolar damage in animal models reminiscent of highly pathogenic H5N1 avian viruses [10,11,12], pregnant women, who exhibited higher case-fatalityratios (CFR) in past influenza pandemics [13,14], and increased admission rates to hospital in seasonal flu [15], have been stressed as a high-risk population for pdm influenza [16]. The purpose of this prospective register-based cohort-study was to characterize the clinical virulence of the pdm (H1N1/09)v during pregnancy in La Reunion

Methods

Results

Conclusion