South Australia reported seven suspected new H5N1 avian influenza cases in greater crested terns along the Limestone Coast on July 27, 2026, deepening an outbreak that has now touched metropolitan Adelaide and crept within 20 kilometres of the Victorian border (The Guardian).

Of the seven suspected cases, one greater crested tern was found at Cape Jaffa, five around Southend Jetty near Beachport, and one at Port MacDonnell. Port MacDonnell sits just over 20 km from the Victorian border. Of the five birds collected from Southend Jetty, four were sick and one was dead. The birds found at Cape Jaffa and Port MacDonnell were both dead (The Guardian).

These seven follow two confirmed H5 detections in greater crested terns in South Australia detected over the weekend prior to July 27. One of those weekend-confirmed cases was the first positive H5 detection in metropolitan Adelaide. If CSIRO verifies the seven suspected cases, the total number of H5 bird flu cases in South Australia would reach 14. Ten of those 14 would be in greater crested terns (The Guardian).

Federal agriculture minister Julie Collins stated that samples from the suspected cases were sent to CSIRO for analysis. South Australia's primary industries minister Clare Scriven addressed the suspected cases publicly on July 27. The state's chief veterinary officer, Dr Skye Fruean, is coordinating the veterinary response (The Guardian).

As of July 27, 2026, there were no H5 detections in poultry or the broader agricultural industry in South Australia. The SA government announced it was stepping up monitoring, including targeted surveillance of areas frequented by greater crested terns (The Guardian).

The national picture is also widening. As of 9:00 am AEST on July 27, Australia had 20 confirmed detections of H5 bird flu in wild seabirds, according to the federal Department of Agriculture (Agriculture.gov.au). Greater crested terns confirmed with H5 were also found at Robe, South Australia, in the state's southeast. South Australia had earlier conducted the largest aerial survey of its coastline in decades in response to the avian influenza situation, an effort announced when the state recorded its second confirmed case (PIRSA). A presentation regarding avian influenza was also delivered to South Australia's State Emergency Centre, as recorded in PIRSA's freedom of information disclosure log (PIRSA FOI disclosure log).

BirdLife Australia chief executive Kate Millar stated the outbreak was "now taking hold and is evidence of spread." Greater crested terns nest in colonies and roost in large flocks, making them particularly vulnerable to H5 avian influenza, according to BirdLife Australia. The suspected cases along the Limestone Coast were located not far from colonies of endangered fairy terns, raising concerns about spillover into already threatened species (The Guardian).

Millar warned that the approaching spring breeding season could create an "engine room of viral spread" as birds gather in large groups at coastal breeding grounds (The Guardian).

The geographic clustering of cases along the Limestone Coast from Cape Jaffa through Beachport to Port MacDonnell traces a contiguous stretch of coastline that doubles as core seabird breeding habitat. The proximity to the Victorian border introduces a cross-jurisdictional dimension: wild bird movement does not respect state lines, and Victorian biosecurity authorities will be watching the Port MacDonnell detection closely. That the outbreak has also reached metropolitan Adelaide, hundreds of kilometres from the Limestone Coast cluster, indicates the virus is not confined to a single focal point.

The concentration of cases in greater crested terns, a species whose colonial nesting behaviour facilitates rapid intraspecies transmission, aligns with patterns observed in H5N1 outbreaks among colonial seabirds elsewhere. If the virus reaches the nearby fairy tern colonies, the consequences for that endangered species could be severe given smaller population sizes and lower genetic resilience.

The zero-detection status in commercial poultry remains the critical buffer between a wildlife event and an agricultural crisis. Australia's poultry industry has navigated H7 outbreaks in recent years, but an H5N1 incursion into commercial flocks would carry different biosecurity and trade implications. The CSIRO confirmation process, typically requiring days rather than hours, means the suspected cases remain provisional. If all seven are confirmed, South Australia's case count would double in a single reporting cycle, and the national total would rise to 27.

The spring breeding season that Millar flags is weeks away in the southern hemisphere. Colonial seabirds converging on coastal breeding grounds could amplify transmission precisely as surveillance resources are stretched across an expanding geographic range. The SA government's targeted surveillance of greater crested tern habitats, combined with the earlier aerial coastline survey, reflects the scale of the monitoring effort. Whether it proves sufficient to detect and contain spread before spring arrival is the operational question facing Dr Fruean's team and their interstate counterparts.