Aboriginal infants in the Northern Territory of Australia experience recurrent otitis media from an early age. Nonencapsulated Haemophilus influenzae (NCHi) colonization of the nasopharynx initially occurs within weeks of birth, persists throughout infancy and most of childhood, and contributes to otitis media. We established previously that the high carriage rates of NCHi in these infants result from concurrent and successive colonization with multiple strains, with sequential elimination of

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... minant strains. We have now sequenced loops 4, 5, and 6 of the NCHi P2 porin gene and characterized several strains with prolonged carriage times. Furthermore, despite a wide diversity of P2 gene sequences, we have four examples of P2 gene identity for strains with different genetic backgrounds as characterized by PCR ribotyping and randomly amplified polymorphic DNA typing, which leads us to suggest that the P2 gene has been transferred between strains. We also discuss the possibility that the paradoxical observation of cocolonization and prolonged carriage of P2-identical strains is related to immune suppression or tolerance in the host.