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Background Although pregnant women are considered at high risk for severe influenza disease, comparative studies of maternal influenza and birth outcomes have not been comprehensively summarised. Objective To review comparative studies evaluating maternal influenza disease and birth outcomes. Search strategy We searched bibliographic databases from inception to December 2014. Selection criteria Studies of preterm birth, small‐for‐gestational‐age (SGA) birth or fetal death, comparing women with and without clinical influenza illness or laboratory‐confirmed influenza infection during pregnancy. Data collection and analysis Two reviewers independently abstracted data and assessed study quality. Main results Heterogeneity across 16 studies reporting preterm birth precluded meta‐analysis. In a subgroup of the highest‐quality studies, two reported significantly increased preterm birth (risk ratios (RR) from 2.4 to 4.0) following severe 2009 pandemic H1N1 (pH1N1) influenza illness, whereas those assessing mild‐to‐moderate pH1N1 or seasonal influenza found no association. Five studies of SGA birth showed no discernible patterns with respect to influenza disease severity (pooled odds ratio 1.24; 95% CI 0.96–1.59). Two fetal death studies were of sufficient quality and size to permit meaningful interpretation. Both reported an increased risk of fetal death following maternal pH1N1 disease (RR 1.9 for mild‐to‐moderate disease and 4.2 for severe disease). Conclusions Comparative studies of preterm birth, SGA birth and fetal death following maternal influenza disease are limited in number and quality. An association between severe pH1N1 disease and preterm birth and fetal death was reported by several studies; however, these limited data do not permit firm conclusions on the magnitude of any association. Tweetable abstract Comparative studies are limited in quality but suggest severe pandemic H1N1 influenza increases preterm birth., Tweetable abstract Comparative studies are limited in quality but suggest severe pandemic H1N1 influenza increases preterm birth.

Background: Breast milk-mediated protection against respiratory viruses is well established. However, protective mechanisms are unclear. Type I interferons (IFN) mediate host defence against respiratory viruses, particularly influenza virus. The relationship among type I IFN, respiratory viral infections and breastfeeding has not been explored. Methods: Type I IFN responses were studied by ELISA and real time PCR in nasal secretions of infants experiencing their first respiratory infection. Modulation of IFN by breastfeeding and other variables affecting severity during viral infection was explored. Results: One hundred and twenty infants were positive by RT-PCR for influenza virus (n = 24), human metapneumovirus (hMPV) (n = 30) or respiratory syncytial virus (RSV) (n = 66). Type I IFNs were detected more frequently in infants infected with influenza virus than in those infected with RSV or hMPV. Breastfeeding promoted higher rates and levels of type I IFN only in infants infected with influenza virus. No effect on IFN production was observed for age, gender or smoking. Conclusion: Our study confirms that type I IFN production is detected more frequently in infants infected with influenza virus. Importantly, higher rates and levels of type I IFN in these infants are associated with breastfeeding. These observations suggest that breast milk can protect against respiratory viruses by activating innate antiviral mechanisms in the host.

Helicobacter pylori strains may be either cagA+ or cagA−, and in logitudinal studies, infection with a cagA+ strain has been associated with increased risk for the development of atrophic gastritis and cancer of the distal stomach. We sought to determine the relative proportion of strains producing CagA in different geographic locales, and the extent to which CagA seroprevalence varied in countries with different gastric and esophageal cancer rates. Using an enzyme-linked immunosorbent assay (ELISA) to detect serum IgG to CagA, we examined sera from 468 asymptomatic H. pylori-infected adults from Canada, Peru, China, Thailand, The Netherlands and 3 different ethnic groups in New Zealand. The CagA seroprevalence in Peru and Thailand (82.2% and 78.8%, respectively) were each substantially higher than for the Chinese (37.9%), Canadian (41.9%), Dutch (39.0%) and New Zealand (28.2%) subjects, but within each population, rates were relatively constant across gender and age groups. Reported gastric but not esophageal cancer rates for the 8 studied populations were significantly associated with H. pylori seroprevalence. Variation in CagA positivity rates was not significantly associated with variation in either gastric or esophageal cancer rates. Our data suggest that CagA seroprevalence is not the major factor influencing gastric cancer rates. Int. J. Cancer 72:453–456, 1997. © 1997 Wiley-Liss, Inc.