Background: Adenovirus type 7 (Ad7) is frequently responsible for severe respiratory infections, especially in young infants. Since the Ad7 epidemics have been associated with severe childhood pneumonia and significant mortality in Korea, 1995-1999, continuous surveillance was necessary for Ad7 related diseases.

Objectives: To characterize epidemiologic features of Ad7 in 1995-2004, genetic diversity of Ad7 were studied by determining genome types (GTs) and the fiber diversity.

Study design: A total of 139 Ad7 strains were obtained from Korean children with pneumonia. Serotype specificity was confirmed by microneutralization assay. GTs were determined by restriction analysis with 12 enzymes. The variable region of the fiber was sequenced.

Results: Two GTs, Ad7d (N=98, 71%) and Ad7l (N=41, 29%) have been identified. In 1995-1996 and 2001-2002, Ad7d was dominant accounting for 98-100% of all Ad7; in 1999-2000, Ad7l was the prevalent GT accounting for 100% of all Ad7; in 1997-1998 and 2003-2004, both GTs circulated concurrently. The change in the relative predominance of GT occurred in 2 or 3 years. The Lys substitution for Arg at codon 280 of the fiber was identified in 31 Ad7d strains (32%) while no variations were observed among Ad7l. It was noteworthy that two fiber variants of Ad7d were not concurrently prevalent on any time after 1996. The shift in predominant fiber variants of Ad7d was also observed in 2-3 years.

Conclusions: Our data demonstrated that the two GTs, Ad7d and Ad7l circulated in an alternating manner between outbreaks of Ad7 associated childhood pneumonia over 10 consecutive years in Korea. Fiber diversity at position 280 within Ad7d appeared to contribute to the annual distribution of Ad7d. This observation necessitates further studies to demonstrate an association between fiber variation and host cell specificity or neutralization antibody recognition.