Critical pertussis: A multi-centric analysis of risk factors and outcomes in Oman

Objectives To identify risk factors and outcomes of patients with critical pertussis. Design Retrospective observational cohort study. Setting Sultan Qaboos University Hospital and The Royal Hospital, Muscat, Oman. Subjects Children aged <13 years presenting to the emergency departments and diagnosed with laboratory-confirmed pertussis by polymerase chain reaction between January 2013 and December 2018. Measurements and main results In total, 157 patients were diagnosed with pertussis, of which 12% ( n = 19) had critical pertussis. Patients with critical pertussis had a higher white blood cell count (WBCC) [adjusted odds ratio (aOR) 1.05; 95% confidence interval (CI) 1.02–1.08; P = 0.003], absolute lymphocyte count (ALC) (aOR 1.08; 95% CI 1.03–1.15; P = 0.004) and absolute neutrophil count (ANC) (aOR 1.05; 95% CI 1.01–1.10; P = 0.032) than patients with non-critical pertussis, even after multi-variate adjustment. The area under the curve for discriminatory accuracy of laboratory variables was 0.75 (95% CI 0.65–0.85), 0.74 (95% CI 0.64–0.84) and 0.72 (95% CI 0.60–0.83) for maximum WBCC, ALC and ANC, respectively, with Youden's cut-off values of 31.5 × 10 9 /L, 19.9 × 10 9 /L and 5.0 × 10 9 /L, respectively. Conclusions In children, higher WBCC, ALC and ANC were significant predictors of critical pertussis. A cut-off level of 31.5 × 10 9 /L for WBCC was associated with critical pertussis.