RESULTS
Clinical and Epidemiologic Analysis
From July 26 to October 7, 2014, we identified 69 patients with EVD that was suspected (3 patients), probable (28 patients), or confirmed (38 patients). Of these patients, 33 were male and 36 were female; 80% of the patients were adults between the ages of 21 and 60 years Among the patients with suspected disease, a higher proportion of children than adults were found to have non-EVD illnesses. Of the 69 patients, 21 male patients and 28 female patients died, including 3 children under the age of 5 years, resulting in a case fatality rate of 74% among probable and confirmed cases, if all cases and deaths were reported. For 28 paired contacts of patients with EVD, the median (serial) interval between dates of the reported onset of symptoms was 16 days (range, 3 to 27), and the mean (±SD) was 16.1±4.4 days, similar to that in West Africa.2 For 32 of the 49 patients who died, the median time from reported symptom onset to death was 11 days (range, 1 to 30), and the mean was 11.3±6.8; the interval was not measured for the other patients who died. All 8 health workers who were affected — 4 with probable EVD and 4 with confirmed EVD — died. As compared with patients with suspected EVD who were found to have non-EVD illnesses, patients with probable or confirmed EVD were more likely to have fever, headache, diarrhea, vomiting or nausea, fatigue, anorexia, muscle pain, difficulty swallowing, conjunctivitis, and blood in stools or vomit This outbreak has been driven by human-to-human transmission, but all cases and contacts appear to have originated from a single index case — in other words, there was no evidence of more than one transfer of infection from an animal reservoir. So far, all cases have been confined to Équateur province, including Boende town (approximately 45,000 inhabitants, with four Health Areas affected), Boende Moke, Bokongo, Lokolia, Lokula, Mondombe, and Watsi Kengo (ranging from 4000 to 12,000 inhabitants), which are situated on or close to road RP314 (Figure 1). The majority of suspected, probable, or confirmed cases of EVD have been reported from Lokolia (39 cases) or Watsi Kengo (18 cases), with only 4 cases reported from Boende town and another 8 from other towns in the district.
The maximum number of cases was reported in the weeks beginning August 17 and 24, according to the date of the onset of symptoms (Figure 2B). It is possible, by plotting the daily case incidence, to discern several generations of cases, as indicated by six peaks in incidence, including the initial index case (Figure 2C). These covered approximately five serial intervals (average, 16.1 days), generating a total of 69 cases in 70 days (Figure 2D).
The rise in case incidence during August was apparently driven by multiple infections acquired from the index case. Of the 29 patients in whom EVD was diagnosed during first 24 days of the outbreak, 21 were reported to be direct contacts of the index case (i.e., they had physical contact or contact with bodily fluids). If all these secondary cases did indeed acquire infection from a single source, this represents a basic case reproduction number2 (R 0) of 21 for this outbreak.
The number of secondary cases arising from each primary case during this outbreak was highly variable. Among other patients with EVD who infected named contacts, 1 patient generated 3 secondary cases, 2 patients generated a further 2 cases each, 30 patients generated a single extra case, and 11 patients generated no further cases. Counting all secondary cases arising among named contacts, including the index case, the average case reproduction number (R) for the whole outbreak was 1.29 (95% confidence interval [CI], −4.71 to 7.29). However, after the exclusion of the 21 cases generated by the index case, the average case reproduction number during the outbreak was 0.84 (95% CI, −0.38 to 2.06), which is below the threshold value for persistent transmission (R>1). This explains the observed decline in the EVD case incidence after mid-August. The last reported patient with EVD became ill on October 4, and no further cases were reported as of October 7.
A total of 1121 contacts of the patients were registered for follow-up. By October 7, a total of 830 had been followed for at least 21 days, which is considered to be the maximum incubation period. The index patient and her contacts had no history of travel to the EVD-affected countries in West Africa (Guinea, Liberia, Nigeria, Senegal, and Sierra Leone) and no history of contact with residents of the affected areas.
RESULTS
Clinical and Epidemiologic Analysis
From July 26 to October 7, 2014, we identified 69 patients with EVD that was suspected (3 patients), probable (28 patients), or confirmed (38 patients). Of these patients, 33 were male and 36 were female; 80% of the patients were adults between the ages of 21 and 60 years Among the patients with suspected disease, a higher proportion of children than adults were found to have non-EVD illnesses. Of the 69 patients, 21 male patients and 28 female patients died, including 3 children under the age of 5 years, resulting in a case fatality rate of 74% among probable and confirmed cases, if all cases and deaths were reported. For 28 paired contacts of patients with EVD, the median (serial) interval between dates of the reported onset of symptoms was 16 days (range, 3 to 27), and the mean (±SD) was 16.1±4.4 days, similar to that in West Africa.2 For 32 of the 49 patients who died, the median time from reported symptom onset to death was 11 days (range, 1 to 30), and the mean was 11.3±6.8; the interval was not measured for the other patients who died. All 8 health workers who were affected — 4 with probable EVD and 4 with confirmed EVD — died. As compared with patients with suspected EVD who were found to have non-EVD illnesses, patients with probable or confirmed EVD were more likely to have fever, headache, diarrhea, vomiting or nausea, fatigue, anorexia, muscle pain, difficulty swallowing, conjunctivitis, and blood in stools or vomit This outbreak has been driven by human-to-human transmission, but all cases and contacts appear to have originated from a single index case — in other words, there was no evidence of more than one transfer of infection from an animal reservoir. So far, all cases have been confined to Équateur province, including Boende town (approximately 45,000 inhabitants, with four Health Areas affected), Boende Moke, Bokongo, Lokolia, Lokula, Mondombe, and Watsi Kengo (ranging from 4000 to 12,000 inhabitants), which are situated on or close to road RP314 (Figure 1). The majority of suspected, probable, or confirmed cases of EVD have been reported from Lokolia (39 cases) or Watsi Kengo (18 cases), with only 4 cases reported from Boende town and another 8 from other towns in the district.
The maximum number of cases was reported in the weeks beginning August 17 and 24, according to the date of the onset of symptoms (Figure 2B). It is possible, by plotting the daily case incidence, to discern several generations of cases, as indicated by six peaks in incidence, including the initial index case (Figure 2C). These covered approximately five serial intervals (average, 16.1 days), generating a total of 69 cases in 70 days (Figure 2D).
The rise in case incidence during August was apparently driven by multiple infections acquired from the index case. Of the 29 patients in whom EVD was diagnosed during first 24 days of the outbreak, 21 were reported to be direct contacts of the index case (i.e., they had physical contact or contact with bodily fluids). If all these secondary cases did indeed acquire infection from a single source, this represents a basic case reproduction number2 (R 0) of 21 for this outbreak.
The number of secondary cases arising from each primary case during this outbreak was highly variable. Among other patients with EVD who infected named contacts, 1 patient generated 3 secondary cases, 2 patients generated a further 2 cases each, 30 patients generated a single extra case, and 11 patients generated no further cases. Counting all secondary cases arising among named contacts, including the index case, the average case reproduction number (R) for the whole outbreak was 1.29 (95% confidence interval [CI], −4.71 to 7.29). However, after the exclusion of the 21 cases generated by the index case, the average case reproduction number during the outbreak was 0.84 (95% CI, −0.38 to 2.06), which is below the threshold value for persistent transmission (R>1). This explains the observed decline in the EVD case incidence after mid-August. The last reported patient with EVD became ill on October 4, and no further cases were reported as of October 7.
A total of 1121 contacts of the patients were registered for follow-up. By October 7, a total of 830 had been followed for at least 21 days, which is considered to be the maximum incubation period. The index patient and her contacts had no history of travel to the EVD-affected countries in West Africa (Guinea, Liberia, Nigeria, Senegal, and Sierra Leone) and no history of contact with residents of the affected areas.
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