Abstract
Background and Aim
From January to June 2025, WA experienced the largest cryptosporidiosis outbreak on record. In response, the WA Department of Health (DoH) investigated notified cases to identify risks factors for illness and detect possible point source outbreaks. This enabled a targeted public health response through public communications, and follow up of aquatic centres (AC) and childcare centres (CC).
Methods and Analysis
Cryptosporidiosis notifications were reported to the DoH by clinicians and laboratories under the Public Health Act, 2016. Cases were sent an SMS survey or interviewed by telephone about travel, visits to AC and CC during their incubation period. Data were analysed descriptively. Cases were diagnosed by Cryptosporidium species PCR, with a subset of case specimens genotyped using the GP60 typing method.
Outcomes
There were 1082 cryptosporidiosis notifications, with 33% of cases <5 years of age and most (86%) cases lived in metropolitan Perth. Surveys were sent to 836 (77%) cases, with 711 (85%) responding. Of the respondents, 7% had travelled interstate or overseas during their incubation period. Of the locally acquired cases, 48% attended an AC, 52% attended a CC, 17% visited both an AC and a CC and 31% reported attending neither an AC or CC. There were 186 cases linked to 14 probable AC outbreaks. There were two probable CC outbreaks. Of the 76 specimens typed, 75 were C. hominis and the most common subtype (n=70) was IeAIIG3T3.
Conclusion and Future Actions
In 2025, WA experienced a large cryptosporidiosis outbreak, with the emergence of a previously rare C. hominis subtype (IeAIIG3T3) in WA. Surveys conducted by SMS were considered an effective means of case follow up. Fourteen AC outbreaks were identified, highlighting the transmission potential at these centres. A high proportion of cases in young children could also contribute to transmission in other settings, especially households.