Assessment of lymphocytosis among pertussis patients in Northwest Ethiopia

Background

Pertussis is a severe and prolonged coughing disease caused by Bordetella pertussis. In 2014, 24.1 million pertussis cases and 160 700 deaths were estimated worldwide in children less than 5 years old. Infection with B. pertussis is frequently characterized by a significant rise in the number of circulating lymphocytes. Thus, the objective of this study was to assess lymphocytosis among pertussis patients in Northwest Ethiopia.

Methods

An institution-based cross-sectional study was conducted among pertussis patients who met the clinical case definition for pertussis. The study was conducted from July 2018 through February 2019 and nasopharyngeal swabs were collected from 321 participants, and samples were analyzed using real-time PCR (RT-PCR). Blood specimens were collected from 321 study participants and total lymphocyte count was conducted using hematology analyzer.

Results

A total of 109 participants were positive for Bordetella species. Lymphocytosis was found in 15/109 (13.8%) of the PCR confirmed pertussis patients. Of those 15 PCR confirmed participants with lymphocytosis, 8/15 (53.3%) had lymphocytosis grading ‘high’ (≥ 2.81/μL) followed by 3/15 (20.0%) ‘moderately high’ (≥ 4.0/μL), and 4/15 (26.7%) had ‘very high’ (≥ 6.0/μL). Among PCR confirmed pertussis participants with lymphocytosis, 11/15 (73.3%) were less than 1 year old.

Conclusions

Despite other co-infections can cause lymphocytosis, this study showed that lymphocyte count could be used to rule out pertussis. Thus, in combination with other specific laboratory tests, lymphocyte count in pertussis suspected patients is recommended.