Serologic Evidence for Cryptococcus neoformansInfection in Early Childhood

Abstract

Objective. Cryptococcus neoformans is an important cause of central nervous system infection in adults with acquired immunodeficiency syndrome (AIDS) but an unusual cause of disease in children with AIDS. The basis for this age-related difference in incidence is not known but may be caused by differences in exposure or immune response. The objective of this study was to determine whether the low prevalence of cryptococcal disease among children is related to a lack of exposure to C neoformans. Methods. Sera were obtained from 185 immunocompetent individuals ranging in age from 1 week to 21 years who were being evaluated in an urban emergency department. Sera were analyzed for antibodies to C neoformans and Candida albicans proteins by immunoblotting. Immunoblot patterns were compared with those obtained from sera of patients with cryptococcosis (n = 10) and workers in a laboratory devoted to the study of C neoformans. The specificity of our results was confirmed by several approaches, including antibody absorption and blocking studies. Sera were also analyzed for the presence of cryptococcal polysaccharide by both enzyme-linked immunosorbent assay and latex agglutination assays. Results. Sera from children 1.1 to 2 years old demonstrated minimal reactivity to C neoformansproteins. In contrast, the majority of sera from children >2 years old recognized many (≥6) C neoformans proteins. For children between 2.1 and 5 years old, 56% of sera (n = 25) reacted with many proteins, whereas for children >5 years old (n = 120), 70% of samples reacted with many proteins. Reactivity was decreased by absorbing sera with C neoformans extracts or by preincubating blots with sera from experimentally infected but not from control rats. Reactivity to C neoformans proteins did not correlate with reactivity to C albicans proteins, which was common in sera from children between the ages of 1.1 and 2 years. Cryptococcal polysaccharide was detected at a titer of 1:16 (∼10 ng/mL) in the sera of 1 child, a 5.6-year-old boy who presented to the emergency department with vomiting. Conclusions. Our findings provide both indirect and direct evidence of C neoformans infection in immunocompetent children. Our results indicate that C neoformans infects a majority of children living in the Bronx after 2 years old. These results are consistent with several observations: the ubiquitous nature of C neoformans in the environment, including its association with pigeon excreta; the large number of pigeons in urban areas; and the increased likelihood of environmental exposure for children once they have learned to walk. The signs and symptoms associated with C neoformans infection in immunocompetent children remained to be determined. Primary pulmonary cryptococcosis may be asymptomatic or produce symptoms confused with viral infections and, therefore, not recognized as a fungal infection. Our results suggest that the low incidence of symptomatic cryptococcal disease in children with AIDS is not a result of lack of exposure toC neoformans. These findings have important implications for C neoformans pathogenesis and the development of vaccine strategies.