Hawke's Bay had the highest rates in NZ in 2019 of a disease dubbed as 'dairy farm fever', which can be fatal if left untreated.
There were 21 cases of leptospirosis in Hawke's Bay DHB's catchment area from January 1 to November 30 last year.
The second highest number of cases was from Waikato, which had 12 cases.
Massey University is leading a study into the disease 'Emerging sources and pathways for leptospirosis', and is asking newly-infected patients in Hawke's Bay to join the study.
The study, led by Dr Shahista Nisa, will look for information which will help prevent the infection.
"It will include measuring the severity of the disease in New Zealanders and how long it lasts, and the best use of animal vaccination and personal protective equipment in order to prevent infection," she said.
The disease can have serious and long-lasting impacts, said Hawke's Bay Medical Officer of Health Nick Jones.
"We need better understanding of leptospirosis to help reduce illness in the future so I encourage anyone contacted regarding this study to seriously consider taking part."
Leptospirosis cases are notified to Public Health, from where requests to join the study will come.
The study states the cumulative data for the last five years (2015-2019) show Waikato DHB having the highest number of cases (n=118) and Hawke's Bay with the second highest number of cases (n=79).
Nisa said leptospirosis could cause prolonged fever and a range of possible systemic complications, including jaundice, renal failure, respiratory insufficiency and confusion.
"Up to 30 per cent of those with acute disease suffer long-term effects such as depression and chronic fatigue and are unable to return to work," she said.
Caused by a bacteria normally caught from contact with the urine of an infected animal, in the first instance leptospirosis can cause flu-like symptoms.
If not treated early, the disease can start to impact on major organs in the body, including the liver, kidneys, heart and lungs.
About 60 per cent of patients with confirmed leptospirosis are hospitalised and about one third suffer life-long effects.
More than half of the people who catch it are farmers or meat workers (who have a very high exposure to animal urine), but others include shearers, hunters and trappers, people handling animal feed that is infected with rodent urine and, more rarely, people who have swum in infected waters.
Records over 18 years show Hawke's Bay is one of the top two areas for leptospirosis hospitalisation.
To avoid catching the disease, people who work in environments where they might come into contact with animal urine are encouraged to wear protective clothing including gloves and eye protection, and to wash hands thoroughly before eating, drinking or smoking.
Farmers are encouraged to vaccinate their animals against the disease.
People in high-risk environments are encouraged to see their GP as soon as possible if they develop flu-like symptoms.