Climate change, Vibrios best friend: an insight in to their relationship and its consequences for public health

Vibrio, a genus of aquatic bacteria, are found globally in warm estuarine and coastal waters that range from low-moderate salinity. Vibrio cholerae, arguably the most famous of the genera, is responsible for cholera epidemics globally. Although, this genus boasts several noteworthy human pathogens such as V. paragemolyticus and V. vulnificus, that cause sporadic gastroenteritis, septicaemia, wound and ear infections.

Sea surface temperature (SST) and sea surface salinity (SSS) are two key environmental factors that influence Vibrio growth and thus number of infections (Baker-Austin et al., 2012). Semenza et al. (2017) looks at using such environmental data to predict where conditions are favourable for Vibrio spp. and hence identify where outbreaks may occur. To predict this threat to public health the European Centre for Disease and Control (ECDC) have created a quasi-real-time map, the ECDC Vibrio Map Viewer, which shows coastal waters with environmental conditions suitable for Vibrio spp. growth.

The authors (Semenza et al., 2017) analysed data from 2006 – 2014 to test using this model and make comparisons between number of reported Vibrio cases and SST. Their study focuses on outbreaks around the Baltic Sea. 117 cases of Vibrio infection were reported between 2006-2014 in Sweden. Refining the data set meant incomplete cases were discounted e.g. discounting 30 patients with no precise place of infection. Leaving them to conduct descriptive statistics and frequency analysis on 56 cases using a case-crossover study (overlaying data of SST and infections). The results showed that SST correlated to observed infections, this relationship was statistically significant (p=0.024). In 2006 and 2014 SST peaked which corresponded to peaks in Vibrio infection. Risk increased significantly when SST passed the 16°C threshold. 50% of all infections were in the ear, 28% were infected wounds and 20% were cases of septicaemia. The only relationship between age and infection risk was that 30% of cases were >60 years old.

They also used climate change projections for SST under the RCP 8.5 and RCP 4.5 scenarios for 2006-2099. Under both climate change scenarios, the number of months with risk of Vibrio transmission increases; the seasonal transmission window expands. There is a significant increase in risk after 2039, this is particularly noticeable in northern latitudes of the Baltic Sea.

The application of these findings could be that we use the ECDC Vibrio Map Viewer during the transmission season to forecast risk, enabling public health authorities to take action to prevent outbreaks, for example closing beaches near high risk areas to prevent swimming. The map can also be used to predict risk conditions in areas where oysters and other shellfish are farmed, temporary farming bans could be enforced.

Studies such as this are important as climate change threatens to increase SST and flood low lying areas, expanding brackish water environments and thus increasing global risk. A few limitations to this study may include the lack of consideration for other factors that contribute to Vibrio growth, e.g. nutrient availability. It also doesn’t consider how responses may vary between species.

References: 

Semenza, J., Trinanes, J., Lohr, W., Sudre, B., Löfdahl, M., Martinez-Urtaza, J., Nichols, G. and Rocklöv, J. (2017). Environmental Suitability of Vibro Infections in a Warming Climate: An early Warning System. Environmental Health Perspectives, 125(10).