KEl Niņo may boost
hepatitis A rates
3 May 2004
El Niņo, the weather pattern
that causes droughts in Australia, has been linked to higher rates of
hepatitis A.
Dr Shilu Tong of the Centre for Health Research at the Queensland University
of Technology and colleagues report their findings in this week's issue of
the Medical Journal of Australia.
Tong and colleagues looked at Australia's incidence of hepatitis A from
January 1991 to December 2000 and how atmospheric pressure seesawed or
oscillated over the same period.
Specifically, the researchers looked at the Southern Oscillation Index (SOI),
a measure of how atmospheric pressure between Darwin and Tahiti changes, a
figure used to calculate the El Niņo Southern Oscillation (ENSO) phenomenon.
"Our results show that the SOI is significantly associated with the
transmission of hepatitis A," Tong told ABC Science Online. "But why El Niņo
events are associated with transmission of hepatitis A, the mechanism,
remains to be determined."
Hepatitis A is a disease that affects the liver and is caused by the
hepatitis A virus, which is passed from person-to-person via contaminated
food or water.
The researchers found that the incidence of hepatitis A cases in Australia
rose a month after a dip in the SOI, indicating warm and dry,
drought-causing conditions.
Tong said that the El Niņo Southern Oscillation had previously been related
to vector-borne and water-borne disease such as cholera and diarrhoea, and
deaths from natural disasters, such as floods, bushfires and cyclones.
"We think our study adds further evidence of El Niņo Southern Oscillation
related health effects," Tong said.
He said while scientists did not know exactly how the weather pattern could
cause an increase in hepatitis A, it was well demonstrated that warmer
weather conditions caused more transmission of food-borne disease.
But a 1997 Sydney outbreak of hepatitis A, linked to eating contaminated
oysters, did not seem to be related to the SOI pattern.
"Our hypothesis is that other factors were responsible for that particular
outbreak," said Tong.
He said the temperature during that year was quite high and this was not
reflected in the SOI because the index only reflected 40% of temperature and
rainfall patterns.