Public health surveillance requires the monitoring of
waterborne disease, but sensitive and
specific detection of relevant incidents is difficult.
The Communicable Disease Surveillance Centre receives
information from various sources
about clusters of cases of illness in England and Wales.
The reporter may suspect that water
consumption or recreational water exposure is the route of
infection, or subsequent
investigation may raise the hypothesis that water is
associated with illness.
It is difficult to prove beyond reasonable doubt that such
a hypothesis is correct. Water
samples from the time of exposure are seldom available,
some organisms are difficult to detect
and almost everyone has some exposure to water. Therefore,
we have developed a method of
categorizing the degree of evidence used to implicate water.
The categories take into account
the epidemiology, microbiology and water quality information.
Thus outbreaks are classified as
being associated with water either
‘strongly’, ‘probably’ or
This system allows a broad database for monitoring possible
effects of water and is not
confined to the few outbreaks which have been intensively
investigated or have positive
environmental microbiology. Thus, for reported incidents,
the sensitivity of classifying it as
water associated should be high but this may be at the
expense of specificity, especially with
the ‘possible’ association.