Ebola hemorrhagic fever transmission and risk factors of contacts, Uganda

Abstract

From August 2000 through January 2001, a large epidemic of Ebola hemorrhagic fever occurred in Uganda, with 425 cases and 224 deaths. Starting from three laboratory-confirmed cases, we traced the chains of transmission for three generations, until we reached the primary case-patients (i.e., persons with an unidentified source of infection). We then prospectively identified the other contacts in whom the disease had developed. To identify the risk factors associated with transmission, we interviewed both healthy and ill contacts (or their proxies)who had been reported by the case-patients (or their proxies) and who met the criteria set for contact tracing during surveillance. The patterns of exposure of 24 case-patients and 65 healthy contacts were defined, and crude and adjusted prevalence proportion ratios (PPR) were estimated for different types of exposure. Contact with the patient's body fluids (PPR = 4.61%, 95% confidence interval 1.73 to 12.29) was the strongest risk factor, although transmission through fomites also seems possible.

Figure

Chains of transmission relative to 27 Ebola cases, Gulu District, Uganda (September–October 2000). The numbers above the blocks indicate the total number of healthy contacts identified for that patient. The slashes indicate patients who died. The isolation ward was opened on October 8. *A laboratory facility for serologic diagnosis of Ebola was set up at Lacor Hospital by the Centers for Disease Control and Prevention on October 21. Description of individual cases follows: 1. AF, young woman, admitted at Gulu Hospital Sept. 19, died the same day. She was buried the following day, next to her parents’ house, without known identified case-patients among those who attended the burial ceremony; 2. OS, son of AF (4 months old); breastfed even during the last days of his mother’s life; admitted to Lacor Hospital; died Sept. 30. 3. OA, father-in-law of AF; nursed his daughter-in-law during the last days of the disease, both at home and in the hospital; reported contact with blood and vomit; died Oct. 7. 4. AR, grandmother of OS; nursed the child after the mother’s death; reported contact with feces and urine; survived. 5. ON, cousin of OA, whom ON touched before and after OA’s death; no reported contacts with body fluid; died Oct. 16. 6. OR, brother of OA; nursed him during last days; reported contacts with feces; died Oct. 17. 7. OJ, brother of ON; used the blanket left by his brother; survived. 8. AE, young woman who sold beer to soldiers; died Sept. 17. 9. OS, son of AE; breastfed; died Sept. 21. 10. AD, mother of AE; nursed her; reported contact with vomit and feces; prepared the dead body; died Oct. 1. 11. AJ, sister of AE; nursed her; reported contact with feces and vomit; prepared the dead body; died Oct. 4. 12. AV, aunt of OS; nursed the child after the mother’s death; reported contact with vomit and feces; died Oct. 11. 13. AN, cousin of OS; they slept together; reported contact with vomit and feces; survived. 14. AV, daughter of AD; nursed her; reported contact with vomit and feces; died Oct. 7. 15. AV, niece of AD; reported direct contact with her during illness; died Oct. 23. 16. AS, daughter of AJ; nursed her, both at home and in the hospital; no reported contact with body fluids; died Oct. 24. 17. AS, co-wife of A J; nursed her; reported contact with blood; died Oct. 24. 18. AE, sister-in-law of AJ; assisted her during delivery on Sept. 28; died Oct. 17. 19. LV, aunt of AJ; assisted her during delivery on Sept. 28; died Oct. 22. 20. OW, son of AJ; born on Sept. 28; died Oct. 9. 21. OJ, husband of LV; nursed her; died Nov. 1. 22. AC, cousin of AV; nursed her; reported contact with feces; survived. 23. AG, young woman; lived next to the barracks; died Oct. 8. 24. AL, sister of AG; nursed her; reported contact with vomit; died Oct. 18. 25. JB, sister of AG; nursed her; reported contact with vomit; died Oct. 26. OR, son of AL; breastfed; died Oct. 21. 27. AF, grandmother of OR; nursed the child after the mother’s death; reported contact with feces and vomit; survived.