Table 2. Estimates of Epidemiologic Variables for Confirmed and Probable Ebola Cases, According to Country, as of September 14, 2014*.
| Variable | All Countries | Guinea | Liberia | Nigeria | Sierra Leone | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| no. of days | no. of patients with data | no. of days | no. of patients with data | no. of days | no. of patients with data | no. of days | no. of patients with data | no. of days | no. of patients with data | |
| Incubation period | ||||||||||
| Single-day exposures | ||||||||||
| Observed† | 9.4±7.4 | 500 | 10.7±8.7 | 35 | 9.5±6.6 | 259 | NC | <10 | 9.0±8.1 | 201 |
| Fitted‡ | 9.1±7.3 | 500 | 9.9±9.8 | 35 | 9.4±6.7 | 259 | NC | <10 | 8.5±7.6 | 201 |
| Multi-day exposures | ||||||||||
| Observed† | 11.4±NA | 155 | 10.9±NA | 20 | 11.7±NA | 79 | NC | <10 | 10.8±NA | 48 |
| Fitted‡ | 9.7±5.5 | 155 | 8.3±4.5 | 20 | 9.9±5.7 | 79 | NC | <10 | 9.9±5.6 | 48 |
| Serial interval§ | ||||||||||
| Observed | 15.3±9.1 | 92 | 19.0±11.0 | 40 | 13.1±6.6 | 26 | NC | <10 | 11.6±5.6 | 25 |
| Fitted¶ | 15.3±9.3 | 92 | 19.0±11.2 | 40 | 13.1±7.8 | 26 | NC | <10 | 11.6±6.3 | 25 |
| R0 ∥ | ||||||||||
| Mean (95% CI) | — | 1.71 (1.44–2.01) | 1.83 (1.72–1.94) | 1.2 (0.67–1.96) | 2.02(1.79–2.26) | |||||
| Doubling time — days (95% CI) | — | 17.53 (13.18–26.64) | 15.78 (14.4–17.37) | 59.75 (13.27–∞) | 12.84 (10.92–15.66) | |||||
| R ** | ||||||||||
| Mean (95% CI) | — | 1.81 (1.60–2.03) | 1.51 (1.41–1.60) | 1.38(1.27–1.51) | ||||||
| Doubling time — days (95% CI) | — | 15.7(12.9–20.3) | 23.6 (20.2–28.2) | NC | 30.2(23.6–42.3) | |||||
| Interval from symptom onset | ||||||||||
| To hospitalization | 5.0±4.7 | 1135 | 5.3±4.3 | 484 | 4.9±5.1 | 245 | 4.1±1.4 | 11 | 4.6±5.1 | 395 |
| To hospital discharge | 16.4±6.5 | 267 | 16.3±6.1 | 152 | 15.4±8.2 | 41 | NC | <10 | 17.2±6.2 | 70 |
| To death | 7.5±6.8 | 594 | 6.4±5.3 | 248 | 7.9±8.0 | 212 | NC | <10 | 8.6±6.9 | 128 |
| To WHO notification | 6.1±8.5 | 2185 | 7.5±10.4 | 743 | 6.0±8.7 | 797 | 3.9±2.3 | 11 | 4.5±5.0 | 634 |
| Interval from WHO notification | ||||||||||
| To hospital discharge | 11.8±7.2 | 312 | 11.1±5.8 | 164 | 11±8.0 | 41 | NC | <10 | 12.7±8.4 | 102 |
| To death | −3.0±13.8 | 584 | −4.4±14.4 | 300 | −1.8±13.6 | 221 | NC | <10 | −1.6±9.2 | 58 |
| Interval from hospitalization | ||||||||||
| To hospital discharge | 11.8±6.1 | 290 | 11±5.4 | 159 | 12.8±8.1 | 40 | NC | <10 | 12.4±5.8 | 86 |
| To death | 4.2±6.4 | 121 | 2.5±3.4 | 36 | 4.5±6.0 | 63 | NC | <10 | 4.4±6.0 | 17 |
| Duration of hospital stay — days†† | 6.42 | 4.99 | 6.72 | NC | 6.88 | |||||
| rate (95% CI) | no. of patients with data | rate (95% CI) | no. of patients with data | rate (95% CI) | no. of patients with data | rate (95% CI) | no. of patients with data | rate (95% CI) | no. of patients with data | |
|---|---|---|---|---|---|---|---|---|---|---|
| Case fatality rate | ||||||||||
| All cases, based on current | 37.7 (36.1–39.2) | 3747 | 57.5 (53.7–61.1) | 677 | 34.7 (32.4–37.1) | 1616 | 40.0 (19.8–64.3) | 15 | 31.6 (29.3–34.1) | 1439 |
| status | ||||||||||
| All cases, based on definitive | 70.8 (68.6–72.8) | 1737 | 70.7 (66.7–74.3) | 542 | 72.3 (68.9–75.4) | 739 | 45.5 (21.3–72.0) | 11 | 69.0 (64.5–73.1) | 445 |
| outcome | ||||||||||
| Before August 18 | 71.3 (68.7–73.7) | 1244 | 68.7 (64.3–72.8) | 454 | 79.8 (75.7–83.4) | 416 | 50.0 (23.7–76.3) | 10 | 65.4 (60.4–70.1) | 364 |
| August 18–September 14 | 59.9 (54.7–64.9) | 354 | 80.7 (71.2–87.6) | 88 | 41.1 (34.3–48.2) | 190 | NC | <10 | 84.0 (74.1–90.6) | 75 |
| All hospitalized cases, based on definitive outcome | 64.3 (61.5–67.0) | 1153 | 64.7 (60.1–68.9) | 450 | 67.0 (62.0–71.7) | 361 | 40.0 (16.8–68.7) | 10 | 61.4 (56.1–66.5) | 332 |
| According to sex | ||||||||||
| Male | 72.2 (69.1–75.1) | 874 | 68.5 (62.6–73.9) | 254 | 74.9 (70.4–79.0) | 395 | NC | <10 | 71.9 (65.7–77.5) | 221 |
| Female | 69.9 (66.7–73.0) | 818 | 72.7 (67.3–77.6) | 286 | 71.6 (66.4–76.3) | 317 | NC | <10 | 64.4 (57.7–70.6) | 208 |
| According to age group | ||||||||||
| <15 yr | 73.4 (67.2–78.8) | 218 | 78.1 (67.3–86.0) | 73 | 70.7 (60.1–79.5) | 82 | NC | <10 | 71.4 (59.3–81.1) | 63 |
| 15–44 yr | 66.1 (63.1–69.0) | 1012 | 64.9 (59.5–69.9) | 319 | 70.6 (66.1–74.8) | 422 | NC | <10 | 61.4 (55.4–67.0) | 264 |
| ≥45 yr | 80.4 (76.2–84.0) | 398 | 78.6 (71.1–84.6) | 140 | 81.1 (74.4–86.4) | 164 | NC | <10 | 82.2 (73.1–88.8) | 90 |
| According to occupation | ||||||||||
| Health care worker | 69.4 (62.1–75.8) | 170 | 56.1 (41.0–70.1) | 41 | 80.0 (68.7–87.9) | 65 | NC | <10 | 68.4 (55.5–79.0) | 57 |
| Non–health care worker | 70.9 (68.6–73.1) | 1567 | 71.9 (67.8–75.6) | 501 | 71.5 (68.0–74.8) | 674 | NC | <10 | 69.1 (64.3–73.5) | 388 |
Plus–minus values are means ±SD. NA denotes not available, NC not calculated, and WHO World Health Organization.
Contacts on day 0 (i.e., on the day of symptom onset) were excluded.
Contacts on day 0 (i.e., on the day of symptom onset) were excluded. Gamma probability distributions were fitted to confirmed and probable cases.
The serial interval is the interval between disease onset in an index case patient and disease onset in a person infected by that index case patient. In this category, the number of patients with data is the number of epidemiologically linked pairs in which the later case patient reported only one direct contact.
Gamma probability distributions were fitted to confirmed and probable cases.
The basic reproduction number (Ro) is the average number of secondary cases that arise when one primary case is introduced into an uninfected population. We estimated the Ro and associated mean doubling time, using a serial interval of 15.3 days, for the period up to March 30, 2014, for Guinea; up to August 24, 2014, for Liberia and Nigeria; and up to July 6, 2014, for Sierra Leone. This number was estimated for individual countries only and not for the combined data.
We estimated R, the mean value of Rt, (the estimated net reproduction number), and associated mean doubling time, using a serial interval of 15.3 days, for the period of July 21 to August 31, 2014. This number was estimated for individual countries only and not for the combined data.
The mean duration of hospital stay was calculated as the weighted average of the observed means from the hospitalization-to-discharge and hospitalization-to-death distributions. This variable was not calculated in Nigeria because there were fewer than 10 case patients with data.