Diagnostic Usefulness of Loop-mediated Isothermal Amplification for Intrafamilial Pertussis Infection

Abstract

　As a Bordetella pertussis gene test, the loop-mediated isothermal amplification (LAMP) method has become widely used for the diagnosis in clinical practice. The diagnostic usefulness of the LAMP method was investigated in 11 infant patients and their 12 families retrospectively, who were judged as having intrafamilial pertussis infection.

　Eleven pediatric patients (Index cases) and their 26 family members (10 families) who developed cough and characteristic symptoms of pertussis, that persisted for 2 weeks or longer and were clinically diagnosed as having pertussis between May 2010 and February 2013, 37 patients in total, were investigated.

　Thirty-three of 37 patients were definitively diagnosed with pertussis and 31 of them (83.4%) were LAMP-positive. Culture and LAMP tests were simultaneously performed in 10 families (26 patients). Among these families, all infants (11 patients) were LAMP-positive, 8 of their siblings, and 10 parents were LAMP-positive, and the positive rate was higher than the culture positive rate. Since LAMP positivity persists for a relatively prolonged period after disease onset, adult patients with atypical symptoms can be diagnosed and the source of pertussis infection in the family can be clarified. The disease through silent transmission may become aggravated when infants have received DTP vaccine. The positive rate on the LAMP test for Bordetella pertussis was higher than that on the culture test, after 4 weeks or more after the onset.

　It should be examined for the asymptomatic family members in the case of the pertussis onset. Because pertussis infection cannot become clear only for a symptom. Additional vaccination of pertussis for adult is necessary even though vaccination has been completed in infancy.