Survey of pertussis infection in infants aged under 3 months with persistent cough

OBJECTIVE: To explore the prevalence of pertussis in hospitalized infants aged under 3 months with persistent cough. METHODS: The nasopharyngeal secretions and serum samples were collected from hospitalized infants aged under 3 months with cough for over 2 weeks from January 2011 to January 2012. The samples of nasopharyngeal secretion were suctioned and collected. Multiplex PCR assay was employed to identify Bordetella pertussis (B. pertussis) and enzyme-linked immunosorbent assay used to detect antibody to pertussis toxin (PT-IgG). Total bacterial DNA was exacted from nasopharyngeal secretion and two-target IS481/PT of B. pertussis was detected by PCR. RESULTS: Fifty-nine infants (32 boys and 27 girls) were enrolled. None of them was pre-immunized with diphtheria-pertussis-tetanus vaccine. Seventeen infants (28.8%) were B. Pertussis positive. Among 17 cases, 3 infants under 1 month, 4 infants 1 -2 months, and 10 infants 2 - 3 months. Three infants had household contacts with persistent cough and their serum antibodies to pertussis toxin were positive. Sixteen infants with pertussis had the paroxysms of frequent and rapid coughs while another 5 with pertussis had long inspiratory effort accompanied by a high-pitched "whoop" at the end of paroxysms. Seven infants with pertussis had conjunctiva bleeding, a special sign of pertussis. Ten infants had lymphocytosis with a predominant elevation of lymphocytes. CONCLUSIONS: B. pertussis is an important pathogen for the infants under 3 months with persistent cough. Multiplex PCR may be used to identify B. pertussis with a high sensitivity. The unrecognized close family members of the infants with pertussis are probably an important source of infection.