SA Health's Chief Medical Officer says that sewage testing at Victor Harbor has returned a "very weak" trace of the COVID-19 virus.

Speaking on ABC Radio Adelaide this morning, Professor Nicola Spurrier downplayed the result, saying that these results come up from time-to-time from routine testing.

Retesting of the samples is underway.

SA Health and SA Water test sewage for fragments of the COVID-19 virus to track infections and provide early warnings of cases in local communities.

An infected person can shed virus in their faeces even if they do not have any symptoms.

Shedding can continue for several weeks after they are no longer infectious.