Human metapneumovirus may be underreported as a pathogen in bronchiolitis and may lead to admittance to intensive care, especially when it infects infants in combination with human respiratory syncytial virus, reported Malcolm G. Semple, M.D., of the University of Liverpool (England), and his associates.
During the 2001–2002 winter season at one hospital, dual infection human metapneumovirus (hMPV) and human respiratory syncytial virus (hRSV) occurred at a significantly higher rate in infants with bronchiolitis who were admitted to the pediatric intensive care unit on mechanical ventilation (72%, 18 of 25) than in infants with bronchiolitis who were sent to the general wards (10%, 15 of 171). The investigators said that the temporal distribution of hMPV infections in infants in the pediatric ICU made it unlikely that the infections were nosocomial. In a subset of infants with complete clinical information, dual infection with hMPV and hRSV was not statistically significantly associated with disease severity in the retrospective study (J. Infect. Dis. 2005;191:382–6).
In nasopharyngeal aspirate and bronchoalveolar lavage samples that were taken at the same time from nine hMPV-infected infants on mechanical ventilation, hMPV was detected in only one nasopharyngeal aspirate and in all nine bronchoalveolar lavages. Of 18 infants who had mechanical ventilation, hMPV infection was found in bronchoalveolar lavages from 15 infants and in nasopharyngeal aspirates from 4 infants.
The discordance in the incidence of hMPV infection detected in bronchoalveolar lavages and nasopharyngeal aspirates raises the possibility that “hMPV infection during endemic seasons may be more common than is currently recognized and that it has been undetected because sampling from the lower respiratory tract is not possible on infants who do not require mechanical ventilation,” Dr. Semple wrote.