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Potentially deadly bacterial populations are growing in numbers throughout the world’s oceans due to global warming. Researchers recently confirmed this for at least one genus called Vibrio, which infects millions of people, killing 142,000 yearly (cholera).

It’s well established that the risk of infection rises with the temperature of water.  For instance, higher temperature boosts the rate of disease and also lengthens the transmission season leading to a higher prevalence of infection or more widespread epidemics. Rita Colwell, a professor at the University of Maryland and the Johns Hopkins Bloomberg School of Public Health and colleagues wanted to know whether there was any relation between water temperature and bacterial abundance in the oceans, the hardest hit by global warming.

The team took advantage of a diligently cared database of plankton samples from nine areas in the North Atlantic and the North Sea collected between 1958 and 2011. In the intervening 50 years since the samples were first collected, the average water temperature rose by 1.5 degrees Celsius. Plankton, small and microscopic organisms drifting or floating in the sea or fresh water, consisting chiefly of diatoms, protozoans, small crustaceans, but also bacteria making the collection ideal for the researchers’ purposes.

Controlling for factors such as water salinity and acidity, the researchers found that the Vibrio bacteria populations, like Vibrio cholerae responsible for the dreadful cholera, do increase with temperature.

“Such increases are associated with an unprecedented occurrence of environmentally acquiredVibrio infections in the human population of Northern Europe and the Atlantic coast of the United States in recent years,” the authors of the paper concluded.

Previously, Finnish researchers showed in 2011 that pathogenic bacterial and parasitic infections become more frequent with increasing temperatures in aquatic systems. Yearly samples taken from two fish farms in northern Finland from 1986 to 2006 show fish tank infections became more prevalent for some bacterial species but dwindled in the case of other types of bacteria.

In Europe and North America where water management systems are robust and reliable, these findings shouldn’t concern people. In developing countries, however, this might mean a serious health hazard because sanitation is poor. Many developing countries are located around the tropics where freak wheater like floods and typhoons are more frequent, making them even more vulnerable to rising bacterial populations.

The researchers advise we monitor plankton in the oceans more carefully using satellite imagery and on-site sampling to assess the risks on a yearly basis. This data will help us adapt and anticipate health risks before they have the chance to develop into disasters.