Published Date: 1998-05-12 23:50:00
Subject: PRO/AH> Cryptosporidiosis - UK (03)
Archive Number: 19980512.0935
CRYPTOSPORIDIOSIS - UK (03)
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A ProMED-mail post
See Also
Cryptosporidiosis - UK 980510215948Cryptosporidiosis - UK (02) 980511200751
[1
Date: Mon, 11 May 1998 14:12:30 +0000
From: Dr. Hukowich <hukowich@EAGLE.CA>
Public health advisories to boil water used for drinking are often the
first line of attack when microbial contamination is found or suspected.
However more specific advice as to the length of time it takes to destroy
pathogenic organisms is either left out or is inconsistent. I have seen
recommendations that vary from 1 minute at a "rolling boil" to 5 minutes to
10 minutes.
Has anyone come across any original research to validate some minimum time
for boiling to destroy the usual pathogens of concern in drinking water
such as cryptosporidia, cholera, typhoid, giardia etc.
--
Alex Hukowich
e-mail: hukowich@eagle.ca
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[2 [This query was referred to Keith Osborn.
Date: Tue, 12 May 1998 20:05:04 +0100
From: Keith Osborn <kosborn@bancroft.u-net.com>
I'm responding to this from home so regrettably I'm away from my references
in the office. Alex's point is extremely pertinent. Our "consensus" view in
the UK (maximum elevation Ben Nevis at 1343 metres a.s.l.) is that merely
bringing to the boil in the standard domestic kettle and allowing to cool
will take care of almost everything of concern. (Our homes generally use an
electric kettle with an automatic shut off when boiling point is reached and
steam is raised: I know you all tend to use the traditional stove-top type.)
This is because it is the time-temperature combination (the area under the
curve) that is important, and obviously it takes a finite time to reach
boiling point and then another finite period to cool again. In my opinion,
10 minutes is simply not justified nor practicable for anyone other than
Himalayan (and Andean?) mountaineers.
Fortunately, although Cryptosporidium oocysts are chlorine resistant, they
are heat sensitive and there is published information showing that they are
no longer infective after 2 minutes around 53 (?) C and 1 minute at 63 (?) C
or so. The act of boiling the water will certainly involve times/
temperatures above these and so boiling is an appropriate response. Though I
can't quote the research off my head, Giardia and the traditional bacterial
pathogens will also be taken care of. The only common waterborne pathogen
about which I can recall some concern is hepatitis A, which is at least
partly heat resistant.
To be an effective public health intervention, "boiling" needs to be a
straight forward task without the need for thermometers and stopwatches.
Some of my public health medical colleagues have expressed reservations
about being too trigger happy when faced with a possible water contamination
incident and have urged us to weigh carefully the risks of diarrhoea in the
community against the very real risks of scalding.
A reference, but I am sure others will have more:
Fayer, R. 1994. Effect of high temperature on infectivity of Cryptosporidium
parvum oocysts in water. Appl. Environment. Microbiol. 60: 2732-2735.
Alex's point is a real concern to those involved in the management of such
responses.
--
Keith Osborn
UK
e-mail: kosborn@bancroft.u-net.com
[Would anyone with specific and targetted references for this problem, send
them to me and I will collate them for a later posting. - Mod.MHJ
........................................mhj/es
--
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