A mysterious illness had baffled health officials and experts after it left 500 people hospitalized and one person dead in southern India.

Dozens of residents in Eluru city in Andhra Pradesh started falling ill on Saturday night, with some losing consciousness.

Symptoms range from epilepsy for 3-5 minutes, memory loss for a few minutes, anxiety, vomiting, headache and back pain, and 546 patients has since been admitted to hospitals.

According to government spokesperson Dasari Nagarjuna, many have recovered and returned home, while 148 are still being treated.

However, a 45-year-old man who was brought in with nausea and seizures had died despite recovering from the epilepsy-like symptoms.

While doctors have not yet been able to identify the illness, preliminary findings revealed that lead and nickel were found to be the cause of the outbreak.

All India Institute of Medical Sciences in New Delhi, National Institute of Nutrition, and Indian Institute of Chemical Technology presented the report to Chief Minister Y.S. Jagan Mohan Reddy on Tuesday.

“More tests are being conducted by Indian Institute of Chemical Technology and other institutes and the results are expected soon,” the report states.

“The Chief Minister directed the authorities to conduct a thorough investigation on the heavy metal content in the patients’ bodies and constantly monitor the treatment process.”

Experts from the World Health Organization, a three-member team drafted by the Union Ministry of Health and Family Welfare arrived in Eluru on Tuesday to collect samples from affected areas.

Deputy Chief Minister for Health A K K Srinivas said the affected people were recovering well and there was no need to panic.

“Full details as to what triggered the mysterious disease will be known only after the central agencies submit their reports,” Srinivas said.

A special sanitation drive has been ordered in Eluru city, as well as nearby rural pockets and Denduluru from where the cases were reported.