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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)

From: Challenges and clinical relevance of molecular detection of Bordetella pertussis in South Africa

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
  1. 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
  2. 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