We retrospectively tested clinical specimens received by NVRL from 29 patients with positive results for HAdV by IF, virus culture, or qPCR during the study period by using specific HAdV-11 and -14 real-time assays. All 29 samples were negative for HAdV-11; however, 9 (31%) samples tested positive for HAdV-14 (Table). All patients sought care or were previously hospitalized during November 2009–July 2010. Of the 9 patients, 7 (78%) were male, 6 (67%) patients were <4 years of age, and the remaining 3 patients were >34 years of age. No epidemiologic links were known between any of the patients. No geographic clustering was observed; the cases were distributed throughout Ireland and involved several hospitals. All respiratory samples were IFA negative for the following respiratory viruses: influenza A, influenza B, parainfluenza viruses 1–3, and respiratory syncytial virus. Our earliest identified HAdV-14–positive specimen (November 10, 2009; case-patient 1 in Table) was positive for influenza A virus by real-time reverse transcription PCR and confirmed as pandemic influenza A (H1N1) 2009 on October 29. No influenza A was detected in a specimen from this patient on November 8 and a nasopharyngeal aspirate collected 2 days later; however, this later specimen was positive for HAdV-14.

Fiber, E1A, and hexon gene sequences derived from the 9 HAdV-14 case-patients from Ireland during the study period were 100% identical for each gene analyzed. These sequences were then compared with subspecies B2 HAdV reference sequences from GenBank, including the prototype de Wit strain, HAdV-14p (5). Phylogenetic analysis demonstrated that the Ireland and US HAdV-14p1 fiber, E1A, and hexon sequences formed a monophyletic group (Figure 1, panels A–C). The sequences from Ireland were 100% identical in the fiber, E1A, and hexon open reading frames (ORFs) to the recently described HAdV-14p1 strains isolated in the United States during 2003–2009 (7–9).The fiber ORF sequences analyzed from the isolates from Ireland were 972 nt, and all contained the 6-nt deletion identified in the recent US HAdV-14p1. This deletion, unique among HAdV B2 strains, corresponds to amino acid residues lysine and glutamic acid (AAA/GAA) at codon positions 251/252 located in the F–G loop of the fiber protein knob. Other than this deletion, the fiber sequences were highly conserved and had 99.3% nt identity to the HAdV-14p de Wit type strain, 99.1% identity to the 11a strains, 99% identity to the Spain 11a/14 strain in 1969, and only 93%–94% similarity to the HAdV-11p strains. The de Wit prototype strain had 99%–99.1% identity to the Spain 11/14 strain 273 from 1969 and other 11a strains, which have been identified as intertypic recombinants with a HAdV-11 hexon gene and a HAdV-14-like fiber gene (7).

Figure 2

Figure 2. Comparative restriction enzyme analysis of viral DNA extracted from the prototype human adenovirus (HAdV) 14 de Wit strain and the first detected HAdV-14 case isolated in Dublin, Ireland, November 2009. All...

The 870 bp of the E1A ORF from the Ireland sequences had higher sequence identity to HAdV-11a strains (99.8%) and the prototype HAdV-14p de Wit strain (99.1%) than to HAdV-11p strains (97%) or any other HAdV B2 reference strains. Furthermore, the Ireland E1A sequences contain a 3-nt insertion, GTG, which is also present in all of the 11a and 14p1 strains but not in the 14p strains. The HAdV-14p1 E1A sequences were most closely associated with the 11a sequences from Taiwan, Singapore, Spain, and the United States, and the fiber sequences from Ireland clustered close to the 11a and 14p sequences. The hexon ORFs analyzed from the samples from Ireland were 2,838 nt and were almost identical (99.86%) to the prototype HAdV-14p de Wit strain. Compared with the E1A and fiber gene sequences, in the hexon region the Ireland sequences exhibited much lower sequence identity to the HAdV-11a and -11p strains analyzed in the study; the HAdV-11a and -11p hexon genes were much more similar to each other and branched separately on the tree (Figure 1, panel C). Viral DNA extracted from each of the 8 isolates of HAdV-14 yielded profiles identical to each other and identical to those reported for the North American strain of HAdV-14. The Ireland isolates were therefore identified as corresponding to genome type 14p1 on the basis of the distinct BclI, BstEII, and PstI restriction patterns (Figure 2).

Of the 9 HAdV-14p1–infected patients, 8 (90%) had respiratory symptoms: pneumonia was diagnosed for 4, bronchiolitis for 3, and acute respiratory distress syndrome (ARDS) for 1. The other patient (case-patient 4; a premature infant born at 35 weeks) was hypotonic at birth with abnormal liver function (Table). Major underlying medical conditions were reported in 4 patients: a BMT recipient; a premature neonate; a patient co-infected with HIV and hepatitis C virus; and a patient with the craniofacial abnormality Pierre Robin syndrome, who had a prior tracheostomy and percutaneous enteral gastrostomy. ARDS developed in the BMT recipient (case-patient 6) 56 days posttransplant; lymphocyte count had not recovered and was at undetectable levels (<0.3/mm³). The patient co-infected with HIV and hepatitis C virus was receiving antiretroviral therapy and had undetectable HIV RNA (<50 copies/mL), a CD4 count of 436 cells/mL (15%), and a resolved hepatitis C virus infection. No underlying conditions were reported for the 5 remaining patients. Three patients died in May 2010: the premature neonate, the BMT recipient, and a 46-year-old woman. The woman had no known notable medical history but had a high body mass index and smoked cigarettes (Table). Two patients (case-patients 4 and 8) received extracorporeal membrane oxygenation. Case-patient 4 had a natural killer (NK) cell deficiency and died. The nature of the NK cell defect in the premature infant was not defined, and bone marrow was analyzed with no pathologic findings noted. Leukocyte screen, however, showed a lack of NK cells; additional screen for immunodeficiencies (such as severe combined immunodeficiency) proved inconclusive, and a human leukocyte antigen–B57–negative haplotype was recorded. Case-patient 8, however, for whom ARDS had been diagnosed, received prolonged (>6 weeks) extracorporeal membrane oxygenation and recovered. Four patients had an unremarkable full recovery.

Of the 9 patients positive for Ireland HAdV-14p1, serum or plasma samples of 2 were submitted for HAdV DNA quantification. The preterm infant (case-patient 4) had a HAdV load in serum of 8.18 log₁₀ viral genomes/mL, and the infant with ARDS (case-patient 8) had a plasma adenoviral load of 8.83 log₁₀ viral genomes/mL. The immunocompetent 46-year-old woman (case-patient 5) had a viral load of 4.80 log₁₀ genomes/g from a postmortem lung biopsy specimen.

We have demonstrated that the HAdV-14p1 strain first identified in the United States is now circulating in Ireland and is associated with substantial illness and with 3 deaths: a BMT recipient, a neonate, and (most notably) an immunocompetent, apparently otherwise healthy adult. The role of HAdV-14p1 in the deaths remains to be elucidated because 2 of the 3 deaths occurred in substantially immunocompromised patients. Conversely, other patients who were also immunocompromised recovered unremarkably, and fatal severe pneumonia and ARDS are known to occur in immunocompetent adults infected with other HAdV serotypes (24). Nevertheless, of concern in the cohort described here is the third death, which occurred in a previously well patient. The immunocompetent woman was a smoker, and smoking has been identified as an independent risk factor possibly facilitating transmission of HAdV-14p1 (11). However, the low rate of infections (5%) observed by Esposito et al. (11) in household contacts of persons infected with the emerging virus suggests that infection is unlikely to spread in the community. Efficient transmission of HAdV-14p1 appears to require close physical contact, as supported by the observation that in barracked communities used for military trainees in the United States, antibody titers demonstrated recent exposure after entry to the facility (25). Of interest in the HAdV-14p1 cases identified in the present study is the higher frequency of male patients (78%) infected; this observation has been reported by other groups (19,26), although the numbers identified in our study are insufficient to make definitive conclusions. Previous reports have noted that prior vaccination with HAdV-7, a subspecies B1 virus, of military recruits may confer cross-protection, presumably from heterotypic immunity, and that this vaccine could potentially be used to reduce HAdV-14p1 disease severity (27,28). Trei et al. have reported on the spread of HAdV-14 in 2007 from a large military training facility in Texas to secondary sites across the United States and to South Korea, despite the institution of active surveillance for acute respiratory disease and prevention and control measures (29). Despite evidence of decreased spread from military personnel to family members outside the training population, many recent military graduates may have been asymptomatic and incubating the virus, which presents a possible scenario for the subsequent dissemination of this virus.

Our findings suggest that clinicians and other health care workers should consider HAdV-14p1 in the differential diagnosis of community-acquired pneumonia. No evidence indicates that HAdV-14p1 infection is substantially more severe than that by other HAdV serotypes; however, we propose increased surveillance for this emerging agent in Europe and elsewhere in immunologically naive populations. In addition, we suggest the retrospective investigation of HAdV-positive specimens for HAdV-14p1, particularly from untyped viruses from patients who had severe disease and who died without an established etiology to help determine the time and location of reemergence of this HAdV in Europe.