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Climate change and microbial risk: Observations from Australia

Climate change and microbial risk: Observations from Australia

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Climate change and microbial risk: Observations from Australia

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  1. Climate change and microbial risk:Observations from Australia Dr David Cunliffe Principal Water Quality Adviser SA Health

  2. Events • Three types of climate driven events have been associated with increased risk of waterborne disease: • Extreme rain • High temperature • Changeable weather • Evidence of increased risk in the absence of catastrophic failure • Causes may be: • direct, through consumption of contaminated drinking water • direct through non-drinking exposure • Indirect due to changes in behaviour

  3. Heavy rainfall • A recurring theme with drinking water outbreaks in intact systems is the influence of heavy rain (or snow-melt). • Outbreaks have been associated with a wide range of microbial agents e.g. Cryptosporidium, Giardia, Toxoplasma Enteroviruses, Norovirus, Hepatitis A, E.coli 0157, Campylobacter and Salmonella • Analysis of acute gastroillness in Wisconsin, USA showed that rainfall was associated with an 11% increase in acute gastrointestinal illness (Drayna et al 2010) • Analysis of outbreaks in the USA (1948-1994) showed that: • 51% of outbreaks were preceded by rainfall events above the 90th%ile • 68% were preceded by events above the 80th%ile • surface water outbreaks associated with rainfall during the same month • groundwater outbreaks associated with a 2 month lag • Curriero et al (2001)

  4. Associated factors • Rainfall alone does not cause outbreaks – in the case of drinking water contaminated water needs to get to consumers. • Sources of organisms: • sewage (viruses, protozoa, bacteria) • livestock (protozoa and bacteria) • native animals (incuding birds) (primarily bacteria but occasionally organisms such as Toxoplasma, Cryptosporidium) • naturally occurring organisms (e.g. Burkholderia pseudomallei) • Entry to system • surface water – across-land flow into waterbodies • groundwater – across land flow directly into bore or transport through aquifers from primary source • treatment failure (lack of treatment, breakdown, incomplete) • distribution system failure (ingress of sewage overflows, bird/small animal faeces in storage tanks)

  5. Cases studies • Milwaukee 1993 • 403,000 cases of Cryptospordiosis • preceded by heavy spring rains and stormwater run-off • contamination of source water overwhelmed the filtration sysytem • led to changes in filtered water turbidity regulations • Walkerton 2000 • 2300 illnesses and 7 deaths from Campylobacter, E.coli 0157 • Preceded by heavy spring rain washing cattle manure into a groundwater supply • System poorly treated and managed • Sydney 1998 • 3 boil water notices over several weeks • heavy rain in catchment increased turbidity and washed livestock waste into source waters. • contamination attributed to Cryptosporidium

  6. High temperatures • Favours growth of naturally occurring pathogens and harmful organisms e.g. Naegleria fowleri, Legionella, Cyanobacteria) • High temperatures can change behaviours influencing the level of risk • Impacts can be exacerbated by drought • Transmission can be through a number of routes including ingestion and inhalation; secondary transmission could be exacerbated

  7. Case study – Naegleria fowleri • Naegleria fowleri: • causative agent of primary amoebic meningitis (rare but almost always fatal) • exposure requires forcing water into the nasal passages • naturally occurring amoeba with a resistant cyst stage • infectious form is sensitive to chlorine and chloramines (preferred choice). • Water is the only known source of infection. Drinking water supplies implicated as an initial source (to swimming pools, garden hoses etc) • Organism is thermophilic and grows at temperatures to 45OC. Cases in Australia typically associated with extended periods of air temperatures exceeding 35OC • Higher temperatures increase growth and threaten barriers (persistent residual) and also likelihood of exposures (increased use of hoses, swimming pools, paddling pools)

  8. Case study - Cryptosporidium • Often see increased cases of GI illness in summer e.g. Salmonella, Campylobacter. Generally considered food-borne. A number of factors including hygiene (i.e. water role) • In the summer of 2007 Sth Australia recorded increased infections with Salmonella, Campylobacter and Cryptosporidium • The Cryptosporidium outbreak was unusual – not typically associated with foodborne disease oubreaks. • Outbreak in summer of 2007 (400 cases in 3-4 months compared to typical annual rate of 100-120)

  9. Waterborne transmission ? • Drinking water not the source – cases supplied from many different sources • But water was involved • A high proportion had used swimming pools (40%). About 60 pools involved • Many reports of multiple cases within families. A number of reports of children sharing bathwater (for water saving) • It was hot and there were reports of infected children using undisinfected paddling pools with other children • Paddling pools not being emptied regularly (water saving)

  10. Case study - cyanobacteria • Decreased water flows in surface water bodies and increased temperatures can produce conditions that are favourable for growth of cyanobacteria • In the last 2-3 years (drought and high temperaures) there has beeen evidence of changed patterns of growth • blooms at different times of the year (two blooms in the River Murray late in the summers of 2009 and 2010) • changes in species. The subtropical/tropical species Cylindrospermopsis is becoming more common in temperate Australia (Murray-Darling) • Drought reduces the availability of alternative sources of water

  11. Summary • There is evidence that the impacts of climate change will provide greater challenges to drinking water supplies and increase risk from enteric pathogens (faecal organisms) and environmental organisms (Naegleria, Burkholderia, cyanobacteria). • Increased risks could be associated with direct impacts from contaminated water or indirect impacts from compromised hygiene. • In both cases there are multiple impacts that will influence outcomes. These include: • awareness of operators of water supplies • management and treatment of water supplies • public education and health promotion