Infants and young children develop infections more frequently than do adults and older children. Infections may be present at birth (see Infections in Neonates) but are more typically contracted afterward. A child's immune system is neither as mature nor as responsive as an adult's, perhaps because of hyporesponsiveness to T-cell–independent antigens, lower immunoglobulin concentrations, a greater proportion of naïve T and B cells compared to memory lymphocytes, or other factors. Children also are exposed to more pathogens from peers in day care centers or school.
Many infectious illnesses that affect infants and children also occur in adults and are discussed elsewhere in The Manual.
Last full review/revision March 2010 by Geoffrey A. Weinberg, MD