Hospitalizations Due to Acute Respiratory Infections in Young Children

Epidemiological data from the New Vaccine Surveillance Network (NVSN) on the incidence of hospitalizations and outpatient visits associated with acute respiratory infections (ARIs) in young children, show rhinovirus and human metapneumovirus (HMPV) are associated with higher hospitalization rates than influenza. The data on these and other ARIs were presented by Kathryn M. Edwards, MD, Vanderbilt University School of Medicine, Nashville, TN, during the 48th annual meeting of the ISDA in Vancouver.

The NVSN is a Centers for Disease Control (CDC)-funded initiative that has been monitoring population-based illness through its centers in Rochester, NY; Nashville, TN; and Cincinnati, OH; for a decade. The network gathers data on resident children who are admitted to county or local hospitals for ARI or fever. The children are enrolled four days per week, following parental consent, and are interviewed, have a chart review, and undergo nasal and throat swabs for culture and polymerase chain reaction (PCR). Outpatient surveillance for ARIs is also undertaken in children under age five during flu seasons, using the same protocols. The total population for the three sites is around 20 million.

“The data on rhinovirus-associated ARI rates of hospitalization are quite remarkable, with 15 per 1000 children aged 0-59 months hospitalized," said Edwards. Of note, rhinovirus was associated with wheezing, and sero-type C in particular is associated with significant wheezing. "Rhinovirus is a trigger for asthma, compared with the rest of the viruses," Edwards said.

"When we looked at HMPV we found that it also has quite a large burden," Edwards said. There was a 4-to-5-person incidence of hospitalizations per 1000 children due to HMPV making it more common than flu.

With respect to influenza, data on rates of hospital admission per thousand children show four admissions per 1000 children during the 2000-2004 flu seasons. The greatest burden of illness was in children aged 0 to 5 months. "Regarding outpatient visits, using the same denominator, there were approximately 100 times more children seen in this setting and about 25 times more seen in the emergency department," Edwards said. Here, the age group most severely impacted was children aged 6-23 months.

The data on parainfluenza (PIV) showed an association with clinical manifestations of wheezing and croup. Importantly, Edwards noted that PIV-1 and PIV-2 caused significantly more croup than PV-3.

“We also looked at human respiratory syncytial virus (RSV) and found it was associated with three times as many hospitalizations compared with the flu," Edwards said. "Outpatient and ED visits were many fold higher." Multiple logistic-regression analysis showed the only risk factors associated with RSV illness requiring hospitalization were age less than two years (particularly those under six months) and a history or prematurity. "One thing that came through very clearly was that the greatest burden of RSV is not in premature infants but in normal, healthy children," she said. "So we can't just target the high-risk children." Hospitalization due to corona virus was minimal, with one per thousand.

In closing, Edwards said that very few of the children went to the intensive care unit, for any of the illnesses, and the only death was associated with a rhinovirus.