A mysterious illness has killed 13 people and sickened 30 others in Liberia since April 23, according to the World Health Organization.

Dr. Alex Gasasira, the WHO’s representative in Liberia, told HuffPost on Saturday that while authorities have not found the “smoking gun” of what has caused the unexplained illnesses and deaths in Sinoe County, Grand Bassa County and the capital city of Monrovia, all signs seem to point to an accidental “poisoning event” of some sort.

On Sunday, Dr. Francis Kateh, Liberia’s deputy health minister and chief medical officer, told HuffPost that initial sample results are pointing to meningitis, but more tests are still being done.

The WHO said on Friday that all tests have come back negative for Ebola or Lassa fever.

Of those that have died, 12 attended the funeral on April 22 or wake the night before for a religious leader in Sinoe County. One lived in the same house as people that had attended the wake or funeral, Kateh told HuffPost. Only one person of the 30 who fell ill remains hospitalized, and she is expected to recover.

“Much of everything is pointing to this poisoning event, but we have not entirely ruled out the possibility of an infectious process,” Gasasira said. “Clinical signs are not completely classical with any common chemical that we have seen as being poisonous in the past, so we continue to follow all leads.”

Gasasira and Kateh said authorities believe that tea drunk at the wake and funeral may be the culprit, as those that consumed the tea have shown an increased association with falling ill and have said it tasted different than it should. However, health authorities were still gathering samples of food and drink from the homes of those who had attended the wake and funeral.

It is common practice in Liberia to contribute food or drink for the wake and funeral and then bring it back to the home ― which is how Gasasira says the other case is believed to have been infected.

The most common symptoms of those that fell ill included abdominal pain, vomiting, weakness, headache, and mental confusion. Some had a hard time breathing and others foamed at the mouth, Gasasira said.

Patients were given oxygen and fluids to treat the dehydration from vomiting. They were also given a broad spectrum antibiotics. Amongst those that have gotten better, an unusual rash around their feet and wrists has developed called petechiae, according to Kateh.

Specimens have been sent internationally to the U.S. Centers for Disease Control and Prevention to determine what agent could be behind the mysterious illness. Gasasira said the results are expected by the middle of next week.

Health authorities are monitoring the other 110 people who attended the wake and funeral, as well as 206 close contacts of all those that have fallen sick, to make sure there are no secondary cases over the next 10-day window.

The rapid response, treatment, and contact tracing in this outbreak is eons apart from the Ebola crisis in 2013, Gasasira said.

“All aspects of the detection investigation and response to this event have been so much better than what we had when we had Ebola,” Gasasira said. “A lot of training has taken place, a lot of investment in strengthening surveillance, communication, ability to conduct investigation in the field, and we are seeing the results of this in Liberia.”

Liberia was declared free of active Ebola transmission last June. That epidemic killed over 11,300 people and infected 28,600 more in Guinea, Sierra Leone and Liberia since 2013.

Kateh stressed he was thankful for the infrastructure built up by the WHO and CDC to help handle a mysterious illness like this. He said that in less than 12 hours, authorities were able to exclude Ebola and Lassa Fever from potential causes.

“This is the key thing that shows that the capacity has been built in the country” to handle potential outbreaks, Kateh said.

This story has been updated to include additional remarks by Dr. Francis Kateh.