Do children with recurrent Haemophilus influenzae otitis media become infected with a new organism or reacquire the original strain?

Using the techniques of outer membrane protein gel analysis and biotyping, we characterized nontypable Haemophilus influenzae isolates from middle ear aspirates of 30 children with recurrent nontypable H, influenzae (NTHI) otitis media. Nine of the 13 children with early recurrence of NTHI otitis (less than 30-day intervals) had respective first and second isolates that were identical. In contrast, 14 of 18 children with late recurrences of NTHI otitis (greater than 30-day intervals) had respective first and second isolates that were different, whereas four children had late recurrences with organisms that appeared to be identical with their respective initial infecting strains. These results suggest that early recurrent NTHI otitis usually is a result of relapse with the initial infecting NTHI strain. In contrast, late recurrent disease is usually the result of infection with a new organism. However, the observation that four children had late recurrences with the original strains suggests that strain-specific protective immunity may not uniformly develop after recovery from NTHI otitis.