A rare family outbreak of infection in immunocompetent fraternal triplets.

Background: () infection is rare in children who were previously healthy, particularly in infants. We present the first report of a family outbreak of infection among immunocompetent infant triplets.

Methods: We reviewed triplets' demographic data, laboratory tests and imaging examinations to describe their clinical features. We performed whole-exome sequencing to rule out primary immunodeficiency disorders. We used DNA sequencing for subspecies identification.

Results: The fraternal triplets (triples A, B and C) presented with a 10-day history of cough. Triple A also experienced a brief episode of fever, and triple B had tachypnea. Chest CT scans showed pulmonary masses and nodules in triples A and C, and cavities in triple B. Cultures of sputum and bronchoalveolar lavage fluid from all triplets yielded . Further subspecies identification showed that isolates from triples A and C were subsp. , and isolates from triple B were subsp. (MAA). After eight months of combination therapy, the pulmonary lesions of the triplets improved significantly.

Conclusion: Our study confirms that pulmonary disease can occur in immunocompetent infants. We hypothesize that the simultaneous infection of the triplets may be associated with their prematurity and extensive environmental exposure. This study highlights the importance to include infection in the differential diagnosis of pulmonary masses and/or cavities, regardless of the age of onset or the presence of underlying pathology or susceptible genes.