From December 2013 to August 11, 2015, a total of 20,035 confirmed and probable cases of Ebola virus disease (EVD) were reported in Guinea, Liberia, and Sierra Leone. There have been concerns that the different cultural roles or physiology of male and female persons may have resulted in the sexes being differently affected during this outbreak.

Data on confirmed, probable, and suspected EVD cases (according to World Health Organization [WHO] case definitions3) were collected with the use of a standard case-investigation form4 in Guinea, Liberia, Nigeria, and Sierra Leone. This form is completed when a case is detected and the patient is admitted to a health care facility as part of the public health response to the outbreak. We used data on confirmed and probable EVD cases in Guinea, Liberia, and Sierra Leone to compare sex-specific epidemiologic patterns. Some records were not complete, but owing to the size and overall detail of the data, we assessed whether there were any differences according to sex.

Within each district, we compared the proportion of the population who were male with the proportion of patients with EVD who were male. For each country, we also tested for sex-related differences in incubation period, time from symptom onset to hospitalization, duration of hospitalization (separately for fatalities and survivors), case fatality rate, clinical signs and symptoms, and reported exposures to sick persons.4,5 We estimated the case fatality rate using recorded final status, excluding data from patients with a date of report on or after the date that the final status was entered into the database, as in our previous reports in the Journal.

Overall, 48.8% of the 20,035 confirmed and probable EVD cases were in male persons. The proportion of patients with EVD who were male (47.3% in Guinea, 50.2% in Liberia, and 48.8% in Sierra Leone) did not differ significantly from the proportion of the population who were male in any country (48.5% in Guinea, 50.0% in Liberia, and 48.2% in Sierra Leone) (Table S1 in the Supplementary Appendix, available with the full text of this letter at NEJM.org). However, the proportions were significantly different in Gueckedou district, Guinea, which had an unusually low proportion of patients who were male (36.6%, P<0.001).

The average interval from symptom onset to hospitalization was approximately 0.5 days shorter among female patients than among male patients in all countries.

Analysis of Confirmed and Probable Cases of Ebola Virus Disease (EVD) in Guinea, Sierra Leone, and Liberia, According to Sex. Driven by cases at the peak of the epidemic (Table S6 in the Supplementary Appendix). Female patients were significantly less likely to die than were male patients (case fatality rate, 63.0% vs. 67.1%; odds ratio, 0.83; 95% confidence interval, 0.77 to 0.91) (Table S8 and Section 3.3 in the Supplementary Appendix). This survival difference remained significant when we adjusted for age group (in 5-year intervals), clinical signs and symptoms, and interval from symptom onset to hospitalization (Section 3.4 in the Supplementary Appendix). In addition, although a higher proportion of female patients than male patients reported an exposure to a sick person, the number of exposures reported by female and male patients did not differ significantly (Section 3.5 in the Supplementary Appendix).

Results did not change significantly when we restricted the analysis to confirmed cases (80.8% of the 20,035 cases). Further details on all results are provided in the Supplementary Appendix.

We found that male and female persons have similar risks, on average, of EVD. However, there were significant differences — in particular, the higher survival rate among female patients. Male patients spent 12.5% longer (approximately 12 hours) on average in the community while symptomatic, which could be particularly important if infectiousness increases after onset, making the risk of transmission in that last half-day higher than average. This suggests that, for control purposes, public health measures to reduce community-based transmission might benefit from awareness of sex-specific differences.

Hamro Doctor