Sydney Water. Why no disease?

Howard Shapiro hms at
Tue Oct 13 17:05:58 EST 1998

Robert Nordon wrote:

Currently the biggest paradox in Sydney is why there has been no outbreak 
of disease (Cryptosporidiosis and Giardiasis) given that levels are so 
high. According to surveys here only about two thirds of the population are 
complying with directions to boil water.

Are the crypto cysts viable?
Are there pathogenic and non-pathogenic species?
Has the community built up resistance over the years?

There seems to be very little discussion addressing these important issues. 
Any ideas?

Beth Rees replied:

>I was at the AFCG  conference and Methods course in Sydney at the time the
>contamination was first announced and I can tell you that I brought home a
>souvenir of the Sydney water supply.  So far I haven't bothered to treat it
>(just stayed close to suitable facilities!) and it seems to subside and
>recurr at about three week intervals.  From my microbiology textbooks, the
>symptoms are pretty typical of giardia - I don't know what crypto is
>supposed to do.  I should also mention a friend who was in Sydney at the
>time also had mild diarrhoea two or three weeks later, and my husband two
>or three weeks after me,my husband acquired ongoing symptoms which are
>compatible with giardia (he's not impressed with the present I brought him)
>and have since responded to a course (3 doses) of tinidazole   .  Maybe it
>only visitors who are susceptible?  Maybe most of the time the symptoms are
>manageable (they can vary from a mild feeling of unwellness to a dramatic
>explosive diarrhoea) and people don't bother going to their doctors so its
>not reported?  Its only notifiable when the diagnosis is confirmed, which
>is pretty hit and miss with giardia - for microscopy three specimens are
>required and are often difficult to detect, and the antigen detection kit
>is expensive.
>So it could be that Sydney people have some resistance, and don't have
>sufficiently dramatic symptoms to visit the doctor.  It would be
>interesting to know how many GPs have simply prescribed treatment without
>attempting to confirm diagnosis.
>Anyone else out there with a souvenir of the methods course?

I was also at the AFCG Meeting and the Methods Course which followed,
and, during the week I was there, I had a nasty bout of what I came
to call the "Anzac Two-Step".  Somebody told me at the time that
there was a lot of that going around.  I got back to normal after a
few days.  It is unlikely that this illness was due to either Giardia
or Cryptosporidium, because 1) both have at least a one-week incubation
period, and I wasn't even in Australia until the day before the meetings
started, and 2) it did not exhibit a prolonged and/or chronic course,
as would diarrhea due to Giardia or Cryptosporidium.  As I recall, the
contamination of the water supply was discovered a day or so after the
Methods Course ended; I was visiting with Hopi Yip, who is involved in
the water testing, and she told me that an alert had just been issued and
that contamination has only been found in samples from downtown Sydney
(I hope Hopi will correct me if my memory has failed on this point).
So, one question which comes to mind is whether infectious levels of the
protozoan parasites were present in the water before contamination was
detected.  Another is whether any substantial number of people developed
diarrhea a week or two after the contamination was detected and assumed
it was due to the same bug that bit me, which had reportedly been going
around for a while when I got to Sydney.  In the U. S., if a story about
contamination of the water supply by Cryptosporidium had hit the news
media, everybody within a 1,000 mile radius of the affected city would
call a lawyer after the first loose bowel movement; I guess there has
been some litigation in Sydney, but probably not what you'd get here.
The bottom line (if you'll pardon the expression) is that not all of the
souvenirs which people may have of the methods course are necessarily due
to protozoan parasites.  To go further with the epidemiology, we'd need
more detailed data about where and when the contamination was detected
in Sydney, and demonstration (or lack of demonstration) of parasites in
samples from the supposedly infected cytometrists.  Maybe we can get B-D
or another commercial entity involved in the reagent development to pay
for the analyses.  Should I write another verse for "King Sh*t"?



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