The influenza-related hospitalization rates of young children with asthma were four times greater than those of children without asthma, and outpatient visits attributable to influenza were about twice as likely among those with asthma, according to Dr. E. Kathryn Miller and her associates.
The results are similar to those of retrospective studies that found that the rate of influenza-attributable outpatient visits for children with asthma and other medical conditions was higher than among healthy children, the investigators noted. But they added that their study may be the first to use prospective, laboratory-confirmed surveillance over several years to estimate rates of influenza-attributable visits for these two groups of children in outpatient settings (Pediatrics 2008;121:1–8).
The investigators conducted a prospective study that included children aged 6–59 months. Patients were either hospitalized between 2000 and 2004 or presented to clinics or emergency departments with acute respiratory illnesses (ARIs) or fever during two flu seasons between 2002 and 2004. In both the hospital and outpatient settings, throat and nasal swabs were obtained and tested for influenza, said Dr. Miller of the department of pediatrics at Vanderbilt University in Nashville, Tenn.
Of the 1,468 children hospitalized, 81 (6%) had lab-confirmed influenza; about one-quarter of these 81 children had asthma. Among children aged 6–23 months, the average annual rate of hospitalizations attributable to influenza was 2.8 cases/1,000 children with asthma, compared with 0.6 cases/1,000 children among healthy children, a significant difference. But the difference was not significant among those children aged 24–59 months: 0.6 cases/1,000 children among those with asthma, compared with 0.2 cases/1,000 children among the healthy children.
Among the 1,432 children enrolled in the outpatient settings, influenza was confirmed in 249 patients (17%); 15% had asthma. Among the children aged 6–23 months with asthma, the average annual rate of outpatient visits attributable to influenza was 316/1,000 children, compared with 152/1,000 children among healthy children. Among those children aged 24–59 months, the rates were 188 cases/1,000 children with asthma, compared with 102 cases/1,000 healthy children in 2003–2004. Both differences were statistically significant.
The authors speculated that possible explanations for the higher rates of inpatient and outpatient visits among children with asthma included their greater susceptibility to influenza and the greater likelihood they will have a more severe influenza-related illness. They also may be more likely to seek medical help for a fever or ARI and may be more likely to be hospitalized because of concerns about their risk of asthma exacerbations, the investigators noted.
Vaccination rates were low in both groups: About 27% of those children with asthma had been vaccinated, and 12%–15% of the children without asthma had been vaccinated, according to parent reports. “Targeted strategies to increase the influenza vaccination rates for both children with asthma and healthy children [aged] 6–59 months are needed,” the researchers said.