Investigation of Anthrax Outbreak, Sierra Leone, May 2022


Background: Anthrax is a contagious zoonotic disease of public health concern. On May 5, 2022, the National Surveillance Program received a notification about suspected cases of anthrax among humans from the Karene District Surveillance Unit, following an anthrax cluster among animals in a neighboring district. We investigated to confirm the diagnosis, determine the magnitude, identify risk factors, and institute control measures.

Methods: A confirmed case was an individual who had the pathognomonic eschar and tested positive for Bacillus anthracis in blood or skin swab. We interviewed case-patients and their families and reviewed medical records to collect data on demographics, clinical, and exposure history with animals or persons with symptoms suggestive of anthrax. We collected blood and swab samples and analyzed using polymerase chain reaction at the Central Public Health Reference Laboratory. We conducted active case searches in affected health facilities and communities.

Results: Nine suspected cases of cutaneous anthrax were identified; five samples were collected from five individuals and were positive for Bacillus anthracis. Three of the confirmed cases were below 10 years old, and three were females. Four cases were reported from Karene and one from Kailahun Districts. All five confirmed cases presented with fever, three with skin lesions and body weakness. Four cases developed symptoms after preparing meat for consumption from sheep which died of unknown causes. Twenty-seven contacts were identified and monitored for 14 days. None developed symptoms. There were no deaths.

Conclusions: This investigation confirmed an anthrax outbreak in Sierra Leone, the first reported since 2018. Preparing sheep meat from sheep that died of unknown causes is the possible source of this outbreak. We enhanced surveillance in affected communities, sensitized communities on anthrax preventive measures, restricted animal movement, burned and buried animal carcasses, and disinfected slaughterhouses. We recommend strengthening animal surveillance including laboratory testing of animal samples to prevent future outbreaks.