At least 21 people have been diagnosed with HIV after a fake doctor reused needles to treat flu patients.

Police in India were hunting Rajendra Yadav who fled the city of Bangarmau in December. He pretended to be a doctor and treated patients for coughs, colds and diarrhoea, according to USA Today.

Yadav cycled between villages in the region and offered to treat sick people. Treatment, which was cheap, almost always involved an injection.

Villagers said they never saw Yadav change the needles he used and health official Sushil Choudhury said that that was the likely cause of the spread of HIV.

"An investigation showed that almost all of them had taken injections from one person," Choudhury said. "This was an important lead. We set up special medical camps in villages in the area and checked 566 people, and 21 were found to be HIV-positive."

According to a UNAids report, two million people in India were living with HIV be the end of 2016. About 9,000 of those were under 15. India has a severe shortage of doctors and it is not uncommon for poor villagers to seek help from people like Yadav.

Raza Hussain Memorial Charitable Trust project manager Mehtab Alam said fake doctors always opted to use glass syringes instead of the disposable type.

"Villagers are ignorant about hygiene," Alam said.