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Paper by Professor Masahiro Hashizume of the Institute of Tropical Medicine Selected as Best Paper by Journal "Epidemiology"

October 16, 2013

A paper by a research team led by Professor Masahiro Hashizume of the Institute of Tropical Medicine was selected as Best Paper (2012) by the journal "Epidemiology." "Epidemiology" is one of the most influential academic journals in the field of epidemiology.

There are usually concerns of potential disease outbreaks following floods, but there have been few reports of actual increases in the number of disease patients, and the actual impact on health of flooding has not been closely investigated. Professor Hashizume's team, together with the London School of Hygiene & Tropical Medicine, International Center for Diarrhoeal Disease Research, Bangladesh, and Research Institute for Humanity and Nature, closely estimated the increases in diarrhea, child respiratory infection (pneumonia, etc.), and mortality rates following major flooding in Bangladesh in 2004.

A follow-up study between 2001 and 2007 of 210,000 residents of the Matlab area, in the delta region of Bangladesh, found that the incidence of diarrhea in the flooded area during the flooding was roughly double that of non-flooded regions. However, the incidence of diarrhea was higher in the flooded region than in the non-flooded region even before the flooding, so, the pre-flooding diarrhea incidence rates in both regions were taken into consideration in order to determine the direct influence of the flooding, and found that the incidence of diarrhea in the flooded region rose 1.5-fold after the adjustment. Furthermore, in the flooded region, the incidence of diarrhea rose in comparison to the non-flooded region during the rainy season, regardless of whether flooding occurred, so seasonal differences were taken into further consideration in order to estimate the direct impact of the floods, and found almost no differences in diarrhea rates between the two regions after the seasonal adjustment. The risk of diarrhea has been believed to increase when flooding occurs, but the team's research found upon close estimation of direct impact that flooding did not produce an increase in the risk of diarrhea. Past research has not taken into consideration differences in disease incidence rates between flooded regions and non-flooded regions before floods, or seasonal disease incidence rates. This research has indicated the necessity of taking factors such as this into careful consideration. The same analysis was performed on mortality rates and rates of child respiratory infections (pneumonia, etc.), and found that while there was no increase in the risk of mortality, the risk of child respiratory infection rose 1.25-fold during the 6 months after the flood.

There are regions which are expected to suffer an increased frequency of flooding due to abnormal weather patterns caused by global climate change. By carefully estimating the rates of disease incidence and mortality caused by flooding, this research is expected to serve as a valuable resource in predicting the health impact of flooding caused by the future climate change.