Oyster growing areas with reticulated sewage and/or waste water treatment plants (WWTP) in the catchment are all potentially affected by closures caused by sewage spills and overflows. Standard risk management practice following such events is to instigate a 21 day closure resulting in lost production, market share, reputational damage, and potential recall costs. The number of growing area closures related to sewage spills and overflows in Australia is significant. In NSW, harvest areas were closed on 100 occasions due to sewage spills between July 2009 and June 2014, resulting in 2688 days of lost sales. The use of FRNA phage as potential indicators of human enteric viruses could lead to a 50% reduction in the number of days closed.
In Tas, there have been 75 harvest area closures of greater than 21 days relating to sewage spills over the past 5 years, resulting in at least 1575 days of lost sales. One three week closure in the Pittwater growing area is estimated to cost approx. $250-$400k combined sales, depending on the season. The cumulative impact of these spills has been estimated to reduce the value of businesses by a combined value of $12 million. Not all sewage incidents result in human enteric viral contamination of shellfish. Factors such as the level of illness in the community, treatment level of waste, size of the spill, hydrodynamics of the growing area, and local growing area conditions all influence the whether a spill results in significant contamination of oysters. FRNA phages have not been used routinely as indicators in shellfish in Australia to date. If FRNA phage levels show contamination is negligible, regulators may allow re-opening of growing areas as early as 10 days after the spill following results from testing on day 7, significantly decreasing the cost of spills to growers. FRNA phages are also showing potential as general indicators of human pathogenic risk.