Cause for concern
On Saturday 25 July, Sydney Water received more positive test results but this time they were considerably elevated. Three central Sydney sites recorded in excess of 100 Cryptosporidium oocysts and Giardia cysts per 100 litres of water. Sydney Water expanded its testing program to include a wider part of the distribution system. Prospect was also re-tested for the first time since 21 July. One of the high readings was obtained from the Crown Street reservoir but, even after a physical check, nothing unusual was discovered.
At 7.50 pm that evening, Sydney Water informed NSW Health of the new developments, pointing out that one of the highest-reading samples from College Street had proved difficult to process. Sydney Water postulated that cysts and oocysts could have collected over years in the biofilm lining of the pipes. These cysts/oocysts may have been dislodged by the flushing of the pipes, thereby releasing them into the system. Sydney Water also explained that first-flush water may not be entirely representative of the whole distribution system, as it may be from a dead-end section of the pipe or a hydrant where contaminated compounds can build up.15 Sydney Water and NSW Health agreed to search for possible local causes of contamination, but none were identified. Both parties also agreed to have the test results independently verified by Macquarie University.
On Sunday, the following day, extremely high results were obtained from Macquarie Street (376C/3952G per 100L), College Street (170C/332G) and the Art Gallery (200C/963G) and lower levels from Crown Street Reservoir (6C/20G). Test results for the Prospect Plant, Potts Hill, Thornleigh and West Ryde were negative; however, the first positive result outside the eastern CBD (except for those at Prospect and Potts Hill) was recorded in Greenacre (0C/8G). Sydney Water immediately began a systematic scouring and flushing of the area affected by the Crown Street reservoir. Meanwhile, Sydney Water’s incident management team continued investigating possible sources of contamination without success. On the basis of visual inspections and other tests, it did not appear that the integrity of the system had been breached.
“In recent years, Cryptosporidium has come to be regarded as one of the most important waterborne human pathogens in developed countries. Over 30 outbreaks associated with drinking water have beenreported in North America and Britain, with the largest infecting an estimated 403,000 people (Mackenzieet al. 1994). Recent research has led to improved methods for testing water for the presence of humaninfectious species, although such tests remain technically demanding and relatively expensive.
Cryptosporidium is an obligate parasite with a complex life cycle that involves intracellular development in the gut wall, with sexual and asexual reproduction. Thick-walled oocysts, shed in faeces are responsible for transmission. Concentrations of oocysts as high as 14,000 per litre in raw sewage and 5,800 per litre in surface water have been reported (Madore et al. 1987). Oocysts are robust and can survive for weeks to months in fresh water under cold conditions (King and Monis 2007).
There are a number of species of Cryptosporidium, with C. hominis and C. parvum identified as the main causes of disease (cryptosporidiosis) in humans. C. hominis appears to be confined to human hosts, while the C. parvum strains that infect humans also occur in cattle and sheep. C. parvum infection sare particularly common in young animals, and it has been reported that infected calves can excrete up to 10 billion oocysts in one day. Waterborne outbreaks of cryptosporidiosis have been attributed to inadequate or faulty treatment and contamination by human or livestock (particularly cattle) waste.
C. hominis and C. parvum can be distinguished from one another and from other Cryptosporidium species by a number of genotyping methods. Infectivity tests using cell culture techniques have also been developed. Consumption of contaminated drinking water is only one of several mechanisms by which transmission (faecal-oral) can occur. Recreational waters, including swimming pools, are an important source of cryptosporidiosis and direct contact with a human carrier is also a common route of transmission.Transmission of Cryptosporidium can also occur by contact with infected farm animals, and occasionally through contaminated food.” ADWG 2011
“Although known as a human parasite for 200 years, Giardia has been regarded seriously as an agent of disease only since the 1960s. It has been identified as an important waterborne pathogen, and linked to many outbreaks of illness associated with drinking water, particularly in North America. Although the importance of this organism has been established, there are large gaps in knowledge about it, and there are no tests for identifying the presence of human infectious species in water.
Giardia has a relatively simple life cycle involving two stages: a flagellate that multiplies in the
intestine, and an infective thick-walled cyst that is shed intermittently but in large numbers in faeces. Concentrations of cysts as high as 88,000 per litre in raw sewage and 240 per litre in surface water havebeen reported (Wallis et al. 1996). Giardia is typically present in larger numbers in Australian sewagethan Cryptsoporidium. Cysts are robust and can survive for weeks to months in fresh water.
There are a number of species of Giardia, but human infections (giardiasis) are usually assigned to one, G. intestinalis (= G. lamblia and G. duodenalis). G. intestinalis infections have been reported from domestic and wild animals, but the host range of human infectious species is uncertain. Although substantial advances have been made in the sampling and counting of cysts, there are currently no established methods to identify human infectious organisms in water. Waterborne outbreaks of giardiasis have generally been linked to consumption of untreated or unfiltered surface water and contamination with human waste.
Consumption of contaminated drinking water is only one of several mechanisms by which transmission (faecal-oral) can occur. Recreational waters, including swimming pools, are also emerging as an important source of giardiasis. However, excluding outbreaks, by far the most likely route of transmission is by direct contact with a human carrier. Transmission of Giardia can also occur by contact with infected animals and occasionally through contaminated food.” ADWG 2011