A laboratory that failed to detect a dangerous toxin in eel meat, which left four people critically ill, is reviewing its procedures after being challenged by public health officials.

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The case, detailed in the latest Public Health Surveillance Report, revealed two men and two women, aged between 41 and 67, were admitted to Wellington Hospital on 8 January with a range of symptoms, from vomiting and diarrhoea to low heart-rates and numbness around their mouths and extremities.

The four victims - three members of the same family and a neighbour - had all eaten contaminated eel brought into the country from Samoa several days previously, and were diagnosed with probable CFP (ciguatera food poisoning).

Health officials retrieved the leftovers from a rubbish bin and they were sent to the Institute of Environmental Science and Research (ESR) for testing.

The company contracted by ESR to do the test initially found no trace of the toxin.

However, after Wellington Regional Public Health questioned the result, the sample was re-tested and high levels of ciguatoxin were found.

According to the report, Regional Public Health was "concerned at the disparity" between the two test results.

ESR said the company was reviewing the tests to check whether it followed correct procedures.

If the inquiry shows the proper protocol was followed in both cases, the investigation will be widened to see if there is a problem with the testing method.

Photo: 123rf

All four patients spent four days in hospital on drips and heart monitors.

This was the second CFP-related outbreak managed by Regional Public Health in the past five years.

In the previous outbreak, six people were poisoned after eating a large reef fish bought from a local retailer.

Officials said the fact the hospital doctor who diagnosed the illness in the latest case was not sure whether CFP was a notifiable disease suggested more awareness among clinicians was needed.

ESR has also asked the Health Ministry to change the case definition of CFP in the Communicable Diseases Control Manual to clarify that it may not always present as a gastro bug, but could manifest itself as a neurological illness.