Human herpesvirus type 6 (HHV-6) infects 90 percent of children by the time they are two years of age. However, few clinical data exist on this condition and no prospective population-based studies have evaluated HHV-6 outside the acute care setting. Zerr and colleagues studied a cohort of 277 healthy infants from birth to two years of age to track HHV-6 acquisition and presentation.

For the prospective, population-based study, the authors recruited participants from obstetricians’ offices. The parents collected weekly saliva samples from their children and kept a daily log of symptoms (i.e., fever, fussiness, rhinorrhea, cough, rash, diarrhea, roseola, febrile seizure). Demographic information also was collected from the participants. The authors analyzed the saliva samples for HHV-6 DNA using polymerase chain reaction (PCR) tests. Primary acquisition was defined as consistent positive PCR results. Acquisition time was defined as the halfway point between the last negative and first positive saliva test. Eighty-one children had well-defined acquisition times and were included in the final analysis. The authors compared the symptoms at acquisition with symptoms closest to illness before and after acquisition.

Primary HHV-6 infection occurred in 130 children (47 percent) by two years of age. Girls and infants with an older sibling were more likely to acquire HHV-6. Day care or playgroup attendance, age of mother at delivery, and season did not affect HHV-6 risk. Ninety-three percent of the 81 children with clear acquisition times had symptoms, although none had febrile seizures (see accompanying table). Thirty-eight percent of symptomatic infants with HHV-6 were examined by a physician for the illness. Infants with primary HHV-6 infection were significantly more likely to have symptoms and see a physician, compared with control infants without infection. Children in this group also were more likely to see a physician for HHV-6 infection than for other illnesses, and the duration of HHV-6 was longer than other illnesses (nine versus three days).

The authors conclude that HHV-6 is a common infection in children two years of age and younger, is usually symptomatic, and often prompts physician visits. Because of the condition’s prominence in this age group, the authors stress the importance of improved diagnostic methods and more effective therapy for HHV-6.