Risk Factors Associated With Severe Influenza Infections in Childhood: Implication for Vaccine Strategy

Abstract

ABSTRACT. Infections caused by influenza virus lead to an excess rate of hospitalization of children during winter months. Current recommendations for vaccination target only children >6 months who belong to specific risk groups.Objective. To identify possible benefits of universal influenza vaccination, this study aims to determine characteristics of children hospitalized at the Montreal Children's Hospital (MCH) because of an infection attributable to influenza virus as well as risk factors associated with hospitalization.Methods. We retrospectively reviewed records of all children with a laboratory-proven diagnosis of influenza seen at MCH between April 1, 1999, and April 1, 2002. Data were analyzed using the Student t test and logistic regression.Results. We identified 182 patients hospitalized because of influenza and 114 patients who were not. Admission diagnoses were suspected sepsis (31%), lower respiratory tract infections (27%), and asthma or bronchiolitis (15%). Mean age of hospitalized patients was 26.1 month (median: 12 months), which was similar to that of patients not hospitalized, and 34% were <6 months. Seventy percent of those hospitalized did not have any underlying medical disorder and only 18% (33) were vaccine candidates according to current recommendations. Of the latter, less than half had been vaccinated. Factors associated with hospitalization were age <12 months (odds ratio [OR]: 2.3; 95% confidence interval [CI]: 1.1-4.8), male gender (OR: 1.9; 95% CI: 1.0 -3.7), dehydration (OR: 4.3; 95% CI: 1.2-16.0), and decreased oxygen saturation (OR: 32.1; 95% CI: 4.1-249).Conclusions. Considering that the majority of children hospitalized for influenza do not belong to the specific risk groups targeted by current recommendations, and that one third are <6 months of age, the target population for vaccination needs to be reexamined. Extending vaccination to all young children, to additional high-risk groups, and to pregnant women has potential to reduce the impact of influenza on children. Pediatrics 2003;112:e197-e201. URL: http://www.pediatrics.org/cgi/ content/full/112/3/e197; influenza, vaccine, pediatrics, and hospitalization.ABBREVIATIONS. MCH, Montreal Children's Hospital; NPA, nasopharyngeal aspirate; DFA, direct immunofluorescent antigen assay; SD, standard deviation; ICU, intensive care unit; IV, intravenous; LOS, length of stay; OR, odds ratio; CI, confidence interval. I nfluenza is a common disease of childhood with the highest morbidity occurring in preschool children. 1-3 Excess hospitalization rates attributable to influenza infections have been estimated to be 104/10 000 child-years for children Ͻ6 months of age, 50/10 000 for children between 6 and 12 months of age and 19/10 000 for children between 1 and 3 years of age. 4 In another study, excess hospitalizations for healthy children Ͻ2 years of age was 86 to 112/100 000 child-months, 5 a rate similar to that reported for adults over 65 years of age. 6 Higher hospitalization rates are reported for children with underlying high-r...

Fatal influenza B virus pneumonia in a preterm neonate: case report and review of the literature

“…Although the platelet count decreased to 50 000/cu.mm, thrombocytopenia is an uncommon finding in influenza infections in children. 11 CRP levels, initially normal, later became elevated. However, elevated CRP levels have been described with influenza infections 7,12 in neonates, making this a poor marker for differentiation from bacterial infections.…”

“…1 Although not seen in our patient, seizures have been described with both influenza A and B in neonates. 7,11 The peripheral white cell count in influenza infection can be variable with normal counts, leucocytosis and leucopenia being all described. 7,11 Our patient had a normal total neutrophil count with a mildly elevated IT ratio.…”

“…7,11 The peripheral white cell count in influenza infection can be variable with normal counts, leucocytosis and leucopenia being all described. 7,11 Our patient had a normal total neutrophil count with a mildly elevated IT ratio. Although the platelet count decreased to 50 000/cu.mm, thrombocytopenia is an uncommon finding in influenza infections in children.…”

“…At our facility, NASBA is routinely used to detect both influenza A and B in respiratory samples using the probes and primers described by Moore et al 15 The advantage of rapid diagnostic tests for influenza is the implementation of infection control measures in a timely manner, and in older children, the early institution of antiviral treatment avoiding unnecessary antibiotics. 3,11 No other neonate in our neonatal intensive care unit (NICU) developed symptoms of influenza and did not need isolation. Our patient was not placed on any antiviral medication.…”

“…3,5 The risk of transmission can be further reduced by encouraging influenza immunization of NICU personnel and other caregivers including parents. 7,11,17 Maternal influenza immunization during pregnancy is another way of protecting neonates against influenza resulting in higher levels of vaccine specific immunoglobulin G antibodies in the newborn. 2 However, preterm infants may not receive sufficient quantities of protective antibodies.…”