There is no question that the most popular time of year to visit the Valley is in winter. This is partly because the rest of the country is experiencing it's worst weather of the year and in contrast, Phoenix seems like summer. So accept that any time after September and before May is probably best.
RSV: RSV in clinical medicine is the abbreviation for respiratory syncytial virus. See: Respiratory syncytial virus.
Serologies are useful in epidemiological surveys. The clinical course of RSV infections is variable. In infants, RSV presents as bronchiolitis. In adults, mild to moderate upper respiratory tract illness is characteristic. However, severe pneumonia can occur, particularly in the elderly with comorbidities or compromised immune status.