Low lymphocyte count: A clinical severity marker in infants with bronchiolitis

Bronchiolitis is the most frequent cause of hospitalization in infants younger than 1 year of age. We sought to evaluate the correlation between lymphocyte count and clinical manifestation in infants hospitalized with bronchiolitis.

We performed a retrospective cohort study evaluating 1297 children hospitalized for bronchiolitis from 2004 to 2019. A nasal washing was tested for 14 respiratory viruses by PCR. A clinical severity score, ranging 0-8, was assigned at hospital admission. History and clinical course were recorded for each infant. Patients were divided in 3 groups according to lymphocyte count tertiles. Parents of enrolled patients have been phoned annually over 5 years to evaluate respiratory sequelae.

A total of 433 children had 2914.2 ± 745.5/mm³ lymphocytes (Group 1), 432 had 4897.6 ± 561.5/mm³ lymphocytes (Group 2) and 432 had 7884 ± 1903.3/mm³ lymphocytes (Group 3). Group 1 patients were more frequently infected by RSV and presented with fever, a worse clinical severity score. They more frequently needed oxygen supplementation, underwent a prolonged hospitalization needed to be admitted to pediatric intensive care unit. Finally, they had more frequently a family history of eczema, wheezing and asthma. We found no differences between lymphocytes count and respiratory sequelae (at least two episodes of wheezing per year).

Infants with low lymphocyte count are more likely to have a worse clinical course of bronchiolitis.