RSV, metapneumovirus, influenza common causes of AOM

Michael E. Pichichero, MD

Every pediatrician knows that ear infections occur in the context of a viral upper respiratory infection nearly every time. Our group and others, when prospectively testing for viral pathogens with AOM, have detected a virus by culture about 40% to 60% of the time. If we add molecular detection methods, then viruses can be identified in about 95% of the cases.

Viral upper respiratory infection causes many changes in the nasopharynx of children that facilitates evolution of asymptomatic bacterial otopathogen colonization to causing middle ear infection. The changes include increased mucus production and thickening of the mucus, decreased cilia beat frequency, and up-regulation of nasal epithelial cell receptors to allow more bacteria to stick to the cells. Moreover, the viral infection down-regulates both the innate immunity system and the adaptive immunity system response that might otherwise control the colonizing bacteria. As a consequence, the bacteria increase in density to an inoculum that can cause disease when the nasal secretions and bacteria mixture reflux up the Eustachian tube and gain entry to the otherwise sterile middle ear space.

The study by the Utah group, led by Carrie Byington, MD, uses a retrospective design to identify an “association” of ear infections with the respiratory season. Not surprisingly, they found an association. The associations were not derived from individual children. Rather, the study used medical records to identify AOM cases and then determined if an increase in cases coincided with viral detection by cultures and enzyme assays, but not the more sensitive molecular techniques that were done in the hospital from submitted samples associated with various illnesses.

A clear association with RSV, influenza and metapneumovirus was found, and this was not novel, as such associations have been previously reported by others.

The investigation failed to detect an association with adenovirus, parainfluenza virus and rhinovirus. The lack of evidence supporting an association with the latter viruses likely is due to the methods of detection and the lack of seasonality of infections due to adenovirus and rhinovirus. Prior reports have shown that both of those viruses can be associated with AOM. As for parainfluenza, it may be that this virus causes fewer of the perturbations in the nasopharynx than the others, so it is not as potent to facilitate AOM.

Clinically, I would agree that fewer ear infections occur in the fall when parainfluenza is circulating than I see in the winter during RSV and influenza season.

Jerome O. Klein, MD

The study by Stockman and colleagues adds to the already extensive literature identifying the role of respiratory viruses in the development of AOM. There are two specific features that are of value in this study. First is the large data set provided by use of the Intermountain Healthcare’s electronic medical record system; the analyses included 96,418 respiratory viral tests over a 9-year period, of which 48% were positive for a viral agent and association with diagnoses of AOM (by ICD-9 codes) in outpatients visits for children aged younger than 18 years.

Second, the use of molecular diagnostic methods that are as sensitive as is currently available and includes ability to identify metapneumoviruses. Although some results differ from prior studies, the message is the same: to decrease the burden of AOM in young children, we need to continue efforts to prevent respiratory viral infections by vaccines or anti-viral therapies. But vaccines for only one agent, the influenza virus vaccine that is currently available, will be insufficient to have a substantial impact on the incidence of middle ear infections. We need a product that includes prevention of the most important agents, as identified in this investigation, RSV and metapneumoviruses, and pathogens identified in other studies including adenoviruses, parainfluenza viruses and rhinoviruses.

Since fiscal considerations are prominent in our current discussions of the future of health care, there is no better place to start than federal support for investigations of preventive methods to reduce the estimated annual $3.5 billion bill for AOM-related health care costs (not to mention that AOM causes pain and decreased hearing for children and distress for parents).