The Effect of Birth Month on RSV Hospitilization
By Hal B. Jenson, MD, FAAP
Dean, Western Michigan University Homer Stryker M.D. School of Medicine, Kalamazoo, MI
Dr. Jenson reports no financial relationships relevant to this field of study.
SYNOPSIS: Compared to manual surveillance methods, an electronic surveillance tool for catheter-associated urinary tract infections had a high negative predictive value but a low positive predictive value.
SOURCE: Wald HL, et al. Accuracy of electronic surveillance of catheter-associated urinary tract infection at an Academic Medical Center. Infect Control Hosp Epidemiol 2014;35:685-91.
The effect of birth month on the risk of respiratory syncytial virus hospitalization in the first year of life in the United States. Pediatr Infect Dis J 2014;33:e135-e140.
A total of 82,296 respiratory syncytial virus (RSV)-related infant (<12 months of age) hospital admissions were identified from statewide inpatient data in five states (Arizona, Iowa, New York, Oregon, and Wisconsin) from July 1996 through June 2006. The relative risk of RSV during the first year of life was determined using an age cohort approach. The overall RSV-related hospital admission rate was 13.9 per 1000 person-years among infants. Among all hospitalized infants, 42% of the infants were female, 73% were <6 months of age, and 3.9% had an underlying condition such as bronchopulmonary dysplasia, cystic fibrosis, or congenital anomaly of the respiratory tract.
In all states, infants born in December and January had approximately 2-3 times greater risk for RSV-related hospitalization during their entire first year of life than infants born in July (RR: 9.8, 95% CI 7.8-12.4). One-month-old infants born between November and February had a significantly increased risk of RSV-confirmed hospitalization compared to one-month old infants born in October; the peak month of risk for one-month-olds was December (RR: 3.30, 95% CI 2.88-3.78). Two-month-olds born in November and December had significantly increased risk of RSV-confirmed hospitalization compared to two-month-olds born in October; the peak month of risk for two-month olds was November (RR: 1.21, 95% CI 1.09-1.35).
In all states, the highest risk for RSV-confirmed hospitalization in the first year of life was among children born between October and February, with the highest risk among one-month-olds who were born between November and March.
Almost all children have at least one symptomatic episode of RSV infection during the first two years of life. Upon first exposure, approximately 25-40% of infants develop clinical signs of bronchiolitis or pneumonia, and 0.5-2.0% require hospitalization, generally infants less than 6 months of age. In the United States, RSV bronchiolitis accounts for 1.5 million outpatient visits among children younger than 5 years of age, and 100,000 to 126,000 hospitalizations among children younger than 1 year of age.
In temperate climates such as the United States, RSV infections peak during winter and early spring, typically with onset in December-January and ending by April-May. The finding that birth-month influences an infant’s risk of serious RSV infection requiring hospitalization indicates that certain cohorts of infants are more vulnerable than others. This provides an opportunity for anticipatory guidance — avoiding ill contacts, early symptoms and signs of bronchiolitis, when to present for care — to parents of those children who are more vulnerable, those who are born between October and February.
There are significant hurdles to RSV vaccine development, including clarity of which immune cell populations or effector molecules are responsible for the clinical manifestations. Testing vaccine candidates will receive intense scrutiny because of the experience in the 1960s when children vaccinated with a formalin-inactivated RSV vaccine developed serious RSV disease upon natural exposure to RSV, including two vaccine-related deaths. In the past 20 years, an attenuated vaccine developed by cold adaptation caused upper respiratory tract congestion and was deemed unacceptable for further development. Recent vaccine candidates based on a combination of mutations and gene deletions, using reverse genetics to manipulate the viral genome, have led to RSV reversions and compensatory mutations. Attenuated RSV vaccines are being tested in adults and children.
The findings of this new study suggest that a strategy that includes maternal vaccination may be necessary to achieve the greatest impact to prevent RSV disease.