Outbreak of acute respiratory infection among infants in Lisbon, Portugal, caused by human adenovirus serotype 3 and a new 7/3 recombinant strain

Abstract

Human adenoviruses (AdVs) typically cause mild illnesses in otherwise healthy hosts. We investigated a pediatric outbreak of acute respiratory infection with fatal outcomes that occurred in Lisbon, Portugal, in 2004. Biological specimens were collected from 83 children attending two nurseries, a kinesiotherapy clinic, and the household of a nanny. Adenovirus infection was confirmed in 48 children by PCR and virus isolation. Most (96%) isolates were classified as being of subspecies B1. Phylogenetic analysis of fiber and hexon gene sequences revealed that most infants were infected with AdV serotype 3 (AdV3) strains. Infants attending one nursery harbored a new recombinant strain containing an AdV serotype 7 hexon and serotype 3 fiber (AdV7/3). Both the AdV3 and the AdV7/3 strains caused fatal infections. Two different serotype 3 strains were circulating in Lisbon in 2004, and the new AdV7/3 recombinant type originated from only one of those strains. These results demonstrate that recombination leads to the emergence of new adenovirus strains with epidemic and lethal potential.

FIG. 1.

Evolutionary relationships of adenovirus isolates. The evolutionary history was inferred by using the maximum-parsimony method and the nucleotide sequences of the hexon (B) and fiber (A) genes. The percentages of replicate trees in which the associated taxa clustered together in the bootstrap test (1,000 replicates) are shown below the branches. Only bootstrap values above 70% are shown. The tree is drawn to scale, and the branch lengths were calculated by using the average pathway method and are in units of the number of changes over the whole sequence. Reference Mastadenovirus genus strains are indicated in italics and are marked by the GenBank accession number, the name of the host, the country of origin in International Organization for Standardization characters (CN, China; KR, Republic of Korea; US, United States of America; CH, Switzerland), and the serotype number. Species names are abbreviated as follows: BAdV, bovine AdV; OAdV, ovine AdV; PAdV, porcine AdV; CAdV, canine AdV; MAdV, mouse AdV; and TSAdV, tree shrew AdV. S, stool; T and ST, tracheal suction; NF, nasopharyngeal. Postmortem tissue types: LLS, left lung section; RLS, right lung section; LLI, liver lobe. Sequences from Portuguese patients are indicated in boldface. Each patient is designated by PA followed by a number. The postmortem tissue used for virus isolation for the deceased patients (patients PA22 and PA27, also designated †) is indicated. The nucleotide at position 93 in the fiber gene (C or G) is indicated in parentheses (see Discussion).