Cryptosporidiosis: A report on
the surveillance and epidemiology of Cryptosporidium
infection in England and Wales
Cryptosporidiosis is a diarrhoeal disease that is commonest in young
children, can infect people of all ages and is severe in people with an
Surveillance has shown a predominantly spring and autumn distribution
of cases over the period 1989 to 2000.
There has been an overall reduction in cryptosporidiosis in the first
half of the year since 2001, but no similar reduction has occurred in
The evidence suggests that the decrease in the first half of the year
is related to improved drinking water quality, particularly in the
North West where substantial new water treatment, including filtration
has been installed to treat supplies that were previously unfiltered.
National infectious disease surveillance provides further evidence, on
top of investigations of Cryptosporidium
outbreaks and analytical studies of sporadic cryptosporidiosis, that
some drinking water supplies have been responsible for a substantial
burden of this diarrhoeal disease over the last few years.
Changes in human infectious disease surveillance indicate that the 1999
regulations have had a significant beneficial impact on waterborne
disease in England and Wales. However, there may still be a burden of
disease associated with drinking water and the epidemiological evidence
is far from clear about the remaining causes of cases.
The routes by which of Cryptosporidium
cases in the second half of the year are infected is unclear, although
swimming and travel both appear to play an important part in the
epidemiology of cryptosporidiosis in this part of the year.
There is evidence that swimming pools within England and Wales are
contributing to an increase in cryptosporidiosis within local
communities in the autumn period. There have been regular examples of
people falling ill on holiday and, this may account for the autumn
incidence of cases and the increased risk of spread of disease.
While travel related cryptosporidiosis has been recognised for years,
two large outbreaks in the UK in different years (2000, 2003)
associated with hotel pools in Majorca appear to have caused cases
across England and Wales. This highlights the potential for
sporadic cases across England and Wales to be related to a common
holiday destination either within England and Wales or further afield.
Outbreaks related to drinking water have declined in recent years but
there are still outbreaks linked to swimming pools and farm visits.
Good up-to-date advice on how to conduct an outbreak investigation
associated with these main routes of infection is desirable.
Monitoring data from at risk sites has shown that a number of water
supplies occasionally contain oocysts. The significance of
these has always been questioned because the oocysts may be non-viable
and may be of a species that is not commonly found in human cases. It
remains possible that low counts of oocysts represent some risk of
Evidence indicates that the routine laboratory staining methods
currently used for screening human faecal samples for Cryptosporidium
oocysts may be missing about a half of all the cases. In addition a
number of hospital laboratories adopt restrictive selection criteria
for testing faecal samples with the results that further cases may not
The genotyping of isolates of Cryptosporidium
to species level has provided clear information on the changing
distribution of the two main species (C. parvum and C. hominis) within
the human population. It has been useful in identifying
species-specific risk factors. There is a strong case for adopting the
strategy of typing all isolates in future.
oocysts at a level below species level has generated much new
information and has the potential to provide new insights into the
transmission of disease.
The improvements in the timeliness and completeness of reporting to
national surveillance have increased the ability to detect national
increases in cases in a timely manner. This improvement needs to
The increase in the capture of the post-code of patients in a way that
does not compromise patient confidentiality allows the ability to
conduct geographic analytical studies that have not previously been
possible. This should allow clearer investigations into the
relationships between the risk status of water supplies and human
Copies of this report may be available as an Acrobat pdf download under the 'Post 2000 Reports' heading on the DWI website.