Objectives: A resurgence of pertussis or whooping cough has been observed worldwide despite broad vaccination coverage. Pertussis like illness (PL I) refers to a clinical syndrome compatible with pertussis infection but lacking laboratory confirmation or an epidemiological link to a confirmed case. Our study aimed to estimate the contribution of Bordetella pertussis infection and identifying predictors of its diagnosis in a cohort of children with PL I. Methods: Demographic and clinical information were retrospectively collected from the medical records of children < 13 years old and hospitalized for PL I in two pediatric units in Oman from 1 January 2012 to 31 December 2013. The laboratory data of all cases were reviewed and confirmed cases of pertussis were identified, analyzed, and compared with non-confirmed cases. Results: A total of 131 patients were enrolled in this study. The majority (95.4% [125/131]) were infants. Only 54.1% (71/131) of admitted children with PL I were tested for pertussis. The incidence of pertussis infection among the tested group was 16.9% (12/71) with a 95% confidence interval 8.2−25.6. Severe illness occurred in 56.4% (74/131) of patients, and six were confirmed to have pertussis. Pediatric intensive care unit admission was required for one confirmed case of pertussis and eight cases from the PL I group (three were negative for pertussis, and five were not tested). Receiver operator characteristic curve analysis revealed that a white blood cell count ≥ 23.5 × 109/L had 96.6% specificity and lymphocytes ≥ 17 × 109/L had 98.3% specificity. Conclusions: Taking into consideration that the number tested for pertussis was limited, the incidence of pertussis was 16.9% (12 out of 71 patients). Lymphocytosis can be used as a reliable predictor for the diagnosis of pertussis especially in the absence of specific confirmatory tests or until their results are available.
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