Iain R. Lake,* Gordon Nichols,†
Graham Bentham,* Florence C.D. Harrison,*
Paul R. Hunter,* and R. Sari Kovats‡
Since new drinking water regulations were implement-
ed in England and Wales in 2000, cryptosporidiosis has
been significantly reduced in the first half of the year but not
in the second. We estimate an annual reduction in disease
of 905 reported cases and ≈6,700 total cases.
reported each year (1). In the 1990s, several cryp-
tosporidiosis outbreaks in England and Wales were associ-
ated with public drinking water supplies; in 2000, new
drinking water regulations were implemented to address
this problem. Risk assessments were required at all water
treatment plants, and those that did not meet the standards
were required to monitor regularly for Cryptosporidium
spp. Consequently, water companies closed some plants,
upgraded others, and paid close attention to the mainte-
nance and operation of their works (2). Since these regula-
tions were implemented, a reduction in reported cases of
cryptosporidiosis, especially the disappearance of the
spring peak, has been reported in northwestern England
(3). The aim of our research was to quantify the public
health impact of the regulations by assessing whether they
have led to statistically significant reductions in cryp-
ryptosporidiosis is a common cause of gastroenteritis
worldwide. In England and Wales, ≈4,500 cases are
All cases of cryptosporidiosis in England and Wales
reported to national surveillance from 1989 through mid-
2005 were analyzed; those associated with recent foreign
travel were excluded. The average weekly number of cryp-
tosporidiosis cases preregulation (1989–1999) were plot-
ted against the same data postregulation (2000–2005)
(Figure). Since the regulations were implemented, fewer
cryptosporidiosis cases have occurred in the first half of
the year but more in the second. However, as the standard
deviation bars on the figure indicate, the number of cases
fluctuated from year to year both before and after the reg-
ulations. This trend makes it difficult to ascertain whether
the changes after regulation are part of the natural interan-
nual variability or represent real changes in incidence. It
also makes it difficult to quantify the public health impact
of the regulations.
Climatic variability and community spread from
imported travel cases are suggested as the main sources of
this interannual variability (4,5). Precipitation may wash
Cryptosporidium organisms from land into public water
supplies, and warm, dry weather may increase the number
of countryside visits. Both of these could result in expo-
sure to Cryptosporidium organisms. Consequently, we
developed a predictive model of weekly cryptosporidiosis
cases using weekly incidence data (1989–1999) and
national data on temperature, rainfall, river discharges, and
reported number of travel-associated cases. Separate mod-
els were produced for different periods of the year.
Ordinary least-squares regression was used for analyses.
The results indicated that between mid-March and the
end of June cryptosporidiosis cases were positively associ-
ated with river discharges that occurred 2 weeks previous-
ly. From July through early September, cryptosporidiosis
was positively associated with warm, dry weather in the
previous 2 months. No associations between cryp-
tosporidiosis and weather existed at other times. Travel
cases were not significant in any of the models. The
detailed methods and results of this analysis are available
from the author. The results are consistent with previous
Comparable data on temperature, rainfall, and river
discharges were obtained for the postregulation period
(2000–2005) and entered into the predictive model. This
estimated the number of cases that would have been
expected, for each week, from 2000 through 2005. To pro-
vide an overview of these predictions, the estimates were
summed to produce totals for each half of the year, for
every year after regulation.
The results are presented in the Table alongside the
95% confidence interval of the prediction, the actual num-
bers of cases reported, and the difference between the actu-
al and predicted cases. In the first half of the year,
cryptosporidiosis was significantly reduced (p<0.05) every
year since 2000. For this finding to be attributable to the
regulations, other factors important in cryptosporidiosis
etiology should have remained constant during this period.
Cryptosporidiosis has been associated with recreational
swimming and person-to-person contact and, to our
knowledge, the levels of these have remained unchanged.
The greatest reduction in cases occurred in the first
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 4, April 2007623
*University of East Anglia, Norwich, UK; †Health Protection
Agency, London, UK; and ‡London School of Hygiene and
Tropical Medicine, London, UK
half of 2001, a period that coincides with the foot-and-
mouth disease epidemic. This epidemic led to the slaugh-
ter of >6 million livestock and restricted public access to
agricultural land (6). The large reduction in cases in 2001
has been attributed to this epidemic (7,8), but our results
indicate that cases were already depressed in the first half
of 2000, and these reductions continued into 2002.
Therefore, the large reduction observed in the first half of
2001 is also likely to be due to the new drinking water
Another reason for lower cryptosporidiosis incidence
since 2000 could be lower levels of Cryptosporidium spp.
in livestock after the foot-and-mouth epidemic (9).
However, a recent study has discounted this (3), and fac-
tors associated with the 2001 epidemic cannot explain the
reductions in cases observed in 2000. We conclude, there-
fore, that improved water treatment associated with the
new drinking water regulations has led to cryptosporidio-
sis reductions during the first half of the year.
In the second half of the year, the pattern is less
straightforward. The numbers of cases are significantly
(p<0.05) lower than predicted in 2001, 2002, and 2004, but
significantly higher (p<0.05) in 2000 and 2003. One expla-
nation for the excess cases in the second half of 2000 and
2003 is that they may represent unreported travel-associat-
ed cases or community transmission from these cases. The
Table demonstrates that many foreign travel–associated
cases occurred in both these periods (>300 in 2000 and
2003 compared with <200 for other years), and these are
poorly recorded in national surveillance (10). This incon-
sistency in the pattern between years, combined with the
potential link between excess cases and travel-associated
cases, led us to conclude that the overall increase in inci-
dence in the second half of the year is not likely to be relat-
ed to the regulations.
By averaging the differences between the observed
and predicted cryptosporidiosis cases across the years, we
can estimate the public health benefits of the regulations.
The average excludes 2001 because of the confounding
effect of the foot-and-mouth epidemic. Since 2000, an
annual average reduction of 615 reported cases has
occurred. This reduction comprises a large decrease in the
624Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 4, April 2007
Figure. Weekly cryptosporidiosis
cases, England and Wales,
1989–1999 and 2000–2005. SD,
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 13, No. 4, April 2007 625 Download full-text
first half of the year and a small increase in the second half.
If we assume that the increase in cases in the second half
of the year is not associated with drinking water, the bene-
fit of the intervention is 905 reported cases per year (the
average reduction in the first half of the year).
Not all cases of cryptosporidiosis in the community
are reported to national surveillance, and the ratio of
reported to community cases is estimated to be 7.4 (11).
This multiplier has uncertainties because it is based upon a
single study. If this multiplier is applied to our estimate of
905 cases, it implies 6,770 fewer cases of cryptosporidio-
sis in the community each year. Two recent reports have
suggested that even this multiplier may be an underesti-
We have presented evidence that new drinking water
regulations implemented in England and Wales during
2000 led to significantly fewer cryptosporidiosis cases in
the first half of the year with no significant change in the
second half of the year. We estimate a reduction in report-
ed cases of 905 per year or ≈6,770 cases in the communi-
ty each year. These findings indicate that regulations such
as those implemented in England and Wales can have a
significant public health benefit in reducing cases of
This research was supported by grants from the Wellcome
Trust (073122/Z/03/Z) and the England and Wales Drinking
Water Inspectorate (DWI 70/2/201).
Dr Lake is a lecturer in environmental sciences at the
University of East Anglia. His research interests include environ-
ment and human health, climate change, and health and geo-
graphic information systems.
1. Health Protection Agency. Cryptosporidium laboratory reports
England and Wales, All identifications, 1986–2005. 2005 [cited
2006 May 1]. Available from http://www.hpa.org.uk/infections/
2. Lloyd A, Drury D. Continuous monitoring for Cryptosporidium—a
novel approach to public health protection. Water Sci Technol.
3. Sopwith W, Regan M, Osborn K, Chalmers R. The changing epi-
demiology of cryptosporidiosis in North West England. Epidemiol
4. Curriero FC, Patz JA, Rose JB, Lele S. The association between
extreme precipitation and waterborne disease outbreaks in the
United States, 1948–1994. Am J Public Health. 2001; 91:1172–4.
5. Lake IR, Bentham CG, Kovats RS, Nichols G. Effects of weather
and river flow on cryptosporidiosis. J Water Health. 2005;3:469–74.
6. Environment Agency. The environmental impact of the foot and
mouth disease outbreak: an interim assessment. Bristol (UK): The
7. Hunter PR, Swift L, Chalmers RM, Syed Q, Hughes LS,
Woodhouse S. Foot and mouth disease and cryptosporidiosis: pos-
sible interaction between two emerging infectious diseases. Emerg
Infect Dis. 2003;9:109–12.
8. Smerdon WJ, Nichols T, Chalmers RM, Heine H, Reacher MH,
Foot and mouth disease in livestock and reduced cryptosporidiosis
in humans, England and Wales. Emerg Infect Dis. 2003;9:22–8.
9. Strachan NJC, Ogden ID, Smith-Palmer A, Jones K. Foot and
mouth epidemic reduces cases of human cryptosporidiosis in
Scotland. J Infect Dis. 2003;188:783–6.
10. Health Protection Agency. Foreign travel-associated illness;
England, Wales, and Northern Ireland—annual report 2005.
London: Health Protection Agency; 2005.
11. Adak GK, Long SM, O’Brien SJ. Trends in indigenous foodborne
disease and deaths, England and Wales: 1992 to 2000. Gut.
12. Chappell CL, Okhuysen PC, Sterling CR, Wang C, Jakubowski W,
Dupont HL. Infectivity of Cryptosporidium parvum in healthy
adults with pre-existing anti-C. parvum serum immunoglobulin G.
Am J Trop Med Hyg. 1999;60:157–64.
13. Frost FJ, Roberts M, Kunde TR, Craun G, Tollestrup K, Harter L, et
al. How clean must our drinking water be: the importance of protec-
tive immunity. J Infect Dis. 2005;191:809–14.
Address for correspondence: Iain R. Lake, School of Environmental
Sciences, University of East Anglia, Norwich, NR4 7TJ, UK;
Cryptosporidiosis Decline, England and Wales
Use of trade names is for identification only and does not imply
endorsement by the Public Health Service or by the U.S.
Department of Health and Human Services.
All those years–almost a hundred–
the farm had hard water.
Hard orange. Buckets lined in orange.
Sink and tub and toilet, too,
once they got running water.
And now, in less than a lifetime,
just by changing the well's location,
in the same yard, mind you,
the water's soft, clear, delicious to drink.
All those years to shake your head over.
Look how sweet life has become;
you can see it in the couple who live here,
their calmness as they sit at their table,
the beauty as they offer you new water to drink.
Copyright 2006 by Sharon Chmielarz. Reprinted by permission of the author through American Life in Poetry, an initiative of Ted Kooser,
the 2004-2006 poet laureate consultant in poetry to the Library of Congress; the American Life in Poetry project is supported by The Poetry
Foundation, The Library of Congress, and the Department of English at the University of Nebraska-Lincoln. Ms Chmielarz's most recent
collection of poems is "The Rhubarb King," Loonfeather Press, 2006.