Climate change linked to increase of cholera cases in Zambia

Apr 23 2009

A study lead by researchers from the Madrid Carlos III Institute of Health associates the increase of cholera cases in Zambia with climatic factors.

For the first time, the results confirm that the increase in environmental temperature six weeks before the rain season increases the number of people affected by this sickness by 4.9%.

"This is the first time that it has become evident in the sub-Saharan region that the increase in environmental temperature is related to the increase in cholera cases¨, explains Miguel Ángel Luque, one of the study's authors and researcher from the Madrid Carlos III Institute of Health (ISCIII), to SINC. Previous studies in Bangladesh already associated the cases with an increase in ocean surface temperature.

The research project, carried out in Lusaka (Zambia) between 2003 and 2006, analyzes data from three cholera epidemics which occurred in a consecutive fashion. The results show that climatic variables (rain and environmental temperature) are related to the increase in cholera cases during the epidemic period.

Experts affirm that cholera has a marked seasonal component associated with the rain season. As such, an increase in temperature six weeks before this period is related with a 4.9% increase in the number of cases of this sickness within the population.

The study maintains that a 1º C increase in temperature six weeks before the beginning of the outbreak explains the 5.2% increase in cholera cases during an epidemic. In the same fashion, if a 50 millimeter rise in precipitation three weeks later is added to this increase, these values would be associated with a 2.5% increase in risk.

¨The climate change is affecting the dynamic and resurgence of infectious sicknesses in a key fashion, concretely malaria and cholera. This year, countries such as Zimbabwe and Zambia are living a devastating cholera epidemic associated with a pandemic process which affects a large part of the continent, and the hypotheses signal that the rise in global temperature is possibly related to the process¨, adds Luque.

The study's limitation is that the model of association between environmental variables and cholera is merely explicative. According to the researcher, ¨It would be ideal to have a predictive method, since the foreseen increase in cases could then be known beforehand, so as to be able to release an early alert in the region and put out a warning to health authorities¨.

Cholera outbreaks continue to be a problem for public health, given that they cause great human, social and economic losses. Just in 2001, the World Health Organization (WHO) and the Global Outbreak Alert & Response Network participated in the verification of 41 cholera outbreaks in 28 countries.

The WHO's data indicates a concerning increase in the number of cholera cases worldwide since the beginning of the 20th century. Although the first pandemic began in 1817 in Asia, it later spread to other parts of the world, such as South America and Africa, ¨cholera's new homeland¨, where it was concentrated in 87% of cases in 2006.

Today, the cholera epidemic's main focus is found in Zimbabwe. Despite the fact that the number of cases has decreased, the mortality rate continues to be elevated in almost all of the provinces, and a real risk exists that the outbreak will be reactivated in some areas. Since the beginning of the outbreak in August of 2008 until March 17th of 2009, 91,164 cases were reported in this country alone, 4,037 of them mortal.