Health workers armed with global positioning systems (GPS) have been helping map the spread of typhoid in Kathmandu, Nepal, described in a 2008 report as ‘the typhoid capital of the world’.

Typhoid is a major public health problem, and taking effective action to curb outbreaks requires careful tracking of cases and how they spread. Tracking outbreaks in Kathmandu has been particularly challenging, as Nepal does not use street names, making it difficult to pinpoint disease clusters.

Researchers used recent advances in DNA sequencing analysis to examine changes in the typhoid genotype, which mutates as it spreads. Plotting the location of outbreaks and mutations on Google Earth showed that disease clusters appear unrelated to population density, and spread was not by direct human to human transmission.

Instead, scientists have identified communal water spouts as the main conduit for contamination. People living at lower water elevation (i.e. downstream) are also at a much higher than average risk of catching the disease.

Dr Jimmy Whitworth, Head of International Activities at the Wellcome Trust, which funded the research, said: "This study, which combines accurate mapping with the latest in genotyping technology, further reinforces the importance of improving the quality of water supplies and infrastructure for sanitation if we are to seriously tackle diseases such as typhoid".

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