Objective To assess whether exposure to high temperatures in pregnancy is associated with increased risk for preterm birth, low birth weight, and stillbirth. Design Systematic review and random effects meta-analysis. Data sources Medline and Web of Science searched up to September 2018, updated in August 2019. Eligibility criteria for selecting studies Clinical studies on associations between high environmental temperatures, and preterm birth, birth weight, and stillbirths. Results 14 880 records and 175 full text articles were screened. 70 studies were included, set in 27 countries, seven of which were countries with low or middle income. In 40 of 47 studies, preterm births were more common at higher than lower temperatures. Exposures were classified as heatwaves, 1°C increments, and temperature threshold cutoff points. In random effects meta-analysis, odds of a preterm birth rose 1.05-fold (95% confidence interval 1.03 to 1.07) per 1°C increase in temperature and 1.16-fold (1.10 to 1.23) during heatwaves. Higher temperature was associated with reduced birth weight in 18 of 28 studies, with considerable statistical heterogeneity. Eight studies on stillbirths all showed associations between temperature and stillbirth, with stillbirths increasing 1.05-fold (1.01 to 1.08) per 1°C rise in temperature. Associations between temperature and outcomes were largest among women in lower socioeconomic groups and at age extremes. The multiple temperature metrics and lag analyses limited comparison between studies and settings. Conclusions Although summary effect sizes are relatively small, heat exposures are common and the outcomes are important determinants of population health. Linkages between socioeconomic status and study outcomes suggest that risks might be largest in low and middle income countries. Temperature rises with global warming could have major implications for child health. Systematic review registration PROSPERO CRD 42019140136 and CRD 42018118113.

Links between heat exposure and congenital anomalies have not been explored in detail despite animal data and other strands of evidence that indicate such links are likely. We reviewed articles on heat and congenital anomalies from PubMed and Web of Science, screening 14,880 titles and abstracts in duplicate for articles on environmental heat exposure during pregnancy and congenital anomalies. Thirteen studies were included. Most studies were in North America (8) or the Middle East (3). Methodological diversity was considerable, including in temperature measurement, gestational windows of exposure, and range of defects studied. Associations were detected between heat exposure and congenital cardiac anomalies in three of six studies, with point estimates highest for atrial septal defects. Two studies with null findings used self-reported temperature exposures. Hypospadias, congenital cataracts, renal agenesis/hypoplasia, spina bifida, and craniofacial defects were also linked with heat exposure. Effects generally increased with duration and intensity of heat exposure. However, some neural tube defects, gastroschisis, anopthalmia/microphthalmia and congenital hypothyroidism were less frequent at higher temperatures. While findings are heterogenous, the evidence raises important concerns about heat exposure and birth defects. Some heterogeneity may be explained by biases in reproductive epidemiology. Pooled analyses of heat impacts using registers of congenital anomalies are a high priority.

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Weather conditions, especially temperature and precipitation, play a critical role in shaping patterns of diarrhoeal diseases. They determine the frequency of outbreaks, and the spatial and seasonal distribution of cases. Not surprisingly, it is anticipated that the burden of diarrhoeal diseases will escalate with climate change, in tandem with gradual increments in mean temperatures, but also during episodic heatwaves. The degree and nature of this escalation will, however, vary with the mix of pathogens in an area, the quality of sanitation services, food hygiene regulations and their enforcement, and the age structure of the population, among other factors. Understanding these patterns can inform the design of measures to prevent and control heat-related diarrhoea. In this editorial, we sum evidence on the heat sensitivity of enteric infections in South Africa (SA) and other parts of sub-Saharan Africa (19 studies), drawing on articles located in a systematic review (methods detailed in Manyuchi et al. [1] ), and consider the implications of these findings for control of diarrhoea in SA in the context of climate change.Several mechanisms underlie the heat sensitivity of microbes. The reproduction, growth and survival rates of most microbes rise with temperature, within certain limits. Higher ambient temperatures accelerate contamination of food across the whole food chain, from preparation, processing and storage to eventual consumption. Importantly, on hot days people spend more time outdoors, and may eat food that is unrefrigerated and is raw or cold, rather than served cooked and hot. [2] Being outdoors also raises exposure to pathogens carried by birds, and farm and wild animals. Rural areas, per se, may be especially susceptible to heat-related impacts on diarrhoea. [3] Further, dust storms, especially frequent on hot and dry days, may settle dust particles with microbial contaminants onto vegetables and other fresh produce. Importantly, if power blackouts occur during hot weather -as we are currently seeing in SA and Venezuela -the integrity of food chains can be compromised, increasing risks of contamination.While 15 of the 19 papers identified in the review reported strong connections between heat exposure and cases of diarrhoea, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] 4 found negligible or even negative associations. [18][19][20][21] This inconsistency illustrates the complexity of pathways between temperature and infectious diseases. Indeed, these correlations are seldom linear and more frequently take an inverted U-shape, where diarrhoea rates rise with temperature, plateau and then decline. Relationships may also be J-shaped, where the incidence of diarrhoea remains stable below a certain temperature threshold, beyond which there is a rapid incline. Moreover, many enteric infections have seasonal patterns: rotavirus cases, for instance, classically occur in winter and campylobacteriosis peaks in spring. [18][19][20] Seasonal patterns are not solely related to climatic factors, however...