Diagnostic challenges and implications of a Yellow Fever co-infected with Malaria case in Freetown, Sierra Leone, September 2023: An outbreak investigation

Introduction: Yellow fever is one of the epidemic-prone and immediately reportable diseases in Sierra Leone. On September 7, 2023, the Western Area Urban District Surveillance Unit received a notification on a suspected yellow fever case from Connaught Hospital. We investigated the case to confirm the diagnosis, identify sources of infection, and institute prevention and control measures. Methods: We interviewed the case patient and his household members. We collected data on demographics, clinical, and travel history using the Ministry of Health case investigation form. We reviewed hospital records and vaccination history. A case was defined as any person residing in Freetown with acute onset of fever and jaundice between August 23 to September 7, 2023. A confirmed case was any person whose sample tested positive for ELISA IgM and or Plaque Reduction Neutralization Test for yellow fever. We conducted an active case search, line-listed 7 contacts, and followed them up for 14 days. Results: The case was a 23-year-old male student who resided in the Tengbeh town community, Freetown. On September 4, 2023, the case developed fever, headache, muscle pain, and jaundice and sought medical treatment at 34 Military Hospital. The case was suspected and tested positive for malaria. He was treated with artesunate, ciprofloxacin, and paracetamol. On September 7, 2023, his condition worsened, and sought further medical attention at Connaught Hospital, where he was suspected of hepatitis B infection, and an abdominopelvic ultrasound scan and serology were conducted. The hepatitis B test was non-reactive. Yellow fever was later suspected, and his blood sample was collected and tested positive for the disease on November 15, 2023. The case had no travel and vaccination history for yellow fever. No additional case was found and none of the contacts developed symptoms. The case is still alive with jaundice symptoms. Conclusion: A yellow fever co-infected with malaria case was confirmed in Freetown albeit a late laboratory diagnosis. The source of the infection was unknown. We sensitized community residents on the regular use of insecticide-treated bed nets and to improve environmental cleaning. We recommended training for healthcare workers, intensifying active case searches, and heightening awareness of yellow fever prevention and control measures.