Table 2.
Comparison of confirmed (N = 56) and possible (N = 38) pertussis cases (real-time PCR positive for IS481 in nasopharyngeal or induced sputum specimens) in hospitalised patients with severe respiratory illness, South Africa, June 2012 – May 2016 (N = 94)
| Characteristic | Confirmed pertussis* n/N# (%) |
Possible pertussis* n/N# (%) |
OR† | P value |
|---|---|---|---|---|
| (95% CI) | ||||
| Year | ||||
| 2012 | 7/56 (12.5) | 4/38 (10.5) | Reference | |
| 2013 | 9/56 (16) | 9/38 (24) | 1.8 (0.4–8.1) | 0.48 |
| 2014 | 16/56 (29) | 13/38 (34) | 1.4 (0.3–5.9) | 0.63 |
| 2015 | 22/56 (39) | 10/38 (26) | 0.8 (0.1–3.4) | 0.76 |
| 2016 | 2/56 (4) | 2/38 (5) | 1.8 (0.2–17.7) | 0.64 |
| Gender | ||||
| Male | 24/56 (43) | 21/38 (55) | Reference | |
| Female | 32/56 (57) | 17/38 (45) | 0.6 (0.3–1.4) | 0.24 |
| Age group (years)¶ | ||||
| < 1 | 23/56 (41) | 9/38 (24) | Reference | |
| 1–4 | 6/56 (11) | 5/38 (13) | 2.1 (0.5–8.2) | 0.29 |
| 5–14 | 5/56 (9) | 2/38 (5) | 1.1 (0.2–6.0) | 0.89 |
| 15–24 | 1/56 (2) | 0/38 (0) | 0.8 (0.03–22.1) | 0.91 |
| 25–44 | 15/56 (27) | 11/38 (29) | 1.8 (0.6–5.4) | 0.27 |
| 45–64 | 4/56 (7) | 11/38 (29) | 6.3 (1.7–23.8) | 0.006 |
| ≥ 65 | 2/56 (4) | 0/38 (0) | 0.5 (0.02–11.3) | 0.66 |
| Fever history | ||||
| No | 28/55 (51) | 21/38 (55) | Reference | |
| Yes | 27/55 (49) | 17/38 (45) | 0.8 (0.4–1.9) | 0.68 |
| HIV status | ||||
| Uninfected | 27/53 (51) | 15/37 (41) | Reference | |
| Infected | 26/53 (49) | 22/37 (59) | 1.5 (0.7–3.6) | 0.33 |
| HIV treatment | ||||
| No | 7/22 (32) | 9/19 (47) | Reference | |
| Yes | 15/22 (68) | 10/19 (53) | 0.5 (0.1–1.8) | 0.31 |
| Symptom duration | ||||
| < 7 days | 35/56 (62.5) | 23/38 (60.5) | Reference | |
| 7–20 days | 10/56 (18) | 5/38 (13) | 0.8 (0.2–2.5) | 0.65 |
| ≥ 21 days | 11/56 (20) | 10/38 (26) | 1.4 (0.5–3.8) | 0.53 |
| Underlying illness‡ | ||||
| No | 50/56 (89) | 30/38 (79) | Reference | |
| Yes | 6/56 (11) | 8/38 (21) | 2.2 (0.7–7.0) | 0.17 |
| ICU | ||||
| No | 53/55 (96) | 37/38 (97) | Reference | |
| Yes | 2/55 (4) | 1/38 (3) | 0.7 (0.06–8.2) | 0.79 |
| Antibiotic treatment (24 h) | ||||
| No | 51/56 (91) | 36/38 (95) | Reference | |
| Yes | 5/56 (9) | 2/38 (5) | 0.6 (0.1–3.1) | 0.10 |
| Hospital duration | ||||
| < 2 days | 5/52 (10) | 5/38 (13) | Reference | |
| 2–4 days | 18/52 (35) | 17/38 (45) | 0.9 (0.2–3.9) | 0.94 |
| 5–7 days | 10/52 (19) | 5/38 (13) | 0.5 (0.1–2.6) | 0.41 |
| ≥ 8 days | 19/52 (36.5) | 11/38 (29) | 0.6 (0.1–2.5) | 0.56 |
| Viral co-infection | ||||
| Viral co-infectionNo | 32/56 (57) | 24/38 (63) | Reference | |
| Viral co-infectionYes | 24/56 (43) | 14/38 (37) | 0.8 (0.3–1.8) | 0.56 |
| Outcome | ||||
| Survived | 50/54 (93) | 37/38 (97) | Reference | |
| Died | 4/54 (7) | 1/38 (3) | 0.3 (0.04–3.1) | 0.34 |
| Vaccination for age§ | ||||
| Full coverage | 16/22 (73) | 10/14 (71) | Reference | |
| Incomplete | 6/22 (27) | 4/14 (29) | 0.9 (0.2–4.2) | 0.93 |
| Facility | ||||
| Edendale | 26/56 (46) | 12/38 (32) | Reference | |
| KTHC | 30/56 (54) | 26/38 (68) | 1.9 (0.8–4.4) | 0.15 |
OR = Odds ratio; CI = confidence interval; KTHC = Klerksdorp Tshepong Hospital complex. *Confirmed case = positive for B. pertussis with IS481 Ct < 35; Possible case = positive for B. pertussis with IS481 35 ≥ Ct ≤ 39. #Data unknown/missing for some cases accounting for the different denominators. †Odds ratio calculated for confirmed versus possible pertussis cases using univariate logistic regression. Bold font indicates statistical significance
‡Patients with previously diagnosed chronic conditions including asthma, chronic lung diseases, cirrhosis/liver failure, chronic renal failure, heart failure, valvular heart disease, coronary heart disease, immunosuppressive therapy, splenectomy, diabetes, burns, kwashiorkor/marasmus, nephrotic syndrome, spinal cord injury, seizure disorder, emphysema, or cancer. §For children ≤5 years of age where vaccine history was available and documented on vaccination card. All percentages are rounded off. ¶ Estimated using penalised logistic regression