Four of the 13 patients who died of a mysterious illness in Liberia since April 23 have tested positive for Neisseria meningitidis serogroup C, a bacterial form of meningitis, according to the U.S. Centers for Disease Control and Prevention.

The news confirmed what Dr. Francis Kateh, Liberia’s deputy health minister and chief medical officer, told HuffPost Sunday.

Additional testing is ongoing to determine if the other deaths and 30 other illnesses in Sinoe County, Grand Bassa County and the capital city of Monrovia following the wake and funeral of a religious leader in Sinoe County are also due to this type of infection.

RELATED COVERAGE 13 Dead From Unexplained Illness In Liberia

According to the CDC’s website, meningitis can be spread by respiratory excretions and saliva. Kateh and Dr. Alex Gasasira, the World Health Organization’s representative in Liberia, told HuffPost on Saturday that tea served at the wake and funeral is suspected in an accidental “poisoning event.”

Those who attended the wake and funeral had a higher likelihood of falling ill if they drank the tea and reported it tasted different than it should have.

Only 1 of the 30 who got ill and survived was still hospitalized as of Saturday.

Patients suffered abdominal pain, vomiting, weakness, headache and mental confusion. Gasasira said some of the patients had a hard time breathing and others foamed at the mouth. According to Kateh, an unusual rash called petechiae has developed around the feet and wrists of those who have recovered.

Senior Press Officer Sharon Hoskins wrote in a statement to HuffPost that the CDC is sending two meningitis laboratory scientists and one meningitis senior epidemiologist to Liberia this week to join the staff from the CDC Country Office in Liberia in the investigation.

On Saturday, Kateh stressed that this infection appears to be localized to those that attended the funeral and wake and one close contact. The CDC also reiterated that there is “no direct threat to the United States.”