Human caliciviruses detected in Mexican children admitted to hospital during 1998-2000, with severe acute gastroenteritis not due to other enteropathogens.

Few studies exist regarding the frequency of human caliciviruses as single etiologic agents in sporadic cases, or in outbreaks occurring in children hospitalized for acute gastroenteritis. In this study, a total of 1,129 children of <5 years of age and hospitalized due to acute diarrhea were enrolled from three main hospitals in Mexico City during a period of 3 years (March 1998 to December 2000). After analyzing all fecal samples for several enteropathogens, 396 stools that remained negative were further screened for human caliciviruses by RT-PCR using a primer set specific to norovirus and sapovirus. Human caliciviruses were detected in 5.6% (22/396) of the children. The minimum incidence rate for 1999 were 5.3% (7/132) for 1999 and 7.8% (13/167) for 2000, since only fecal specimens that tested negative to other enteric pathogens were examined. Positive samples were further characterized using specific GI and GII primers and sequencing. Norovirus GII was detected in 19/22 samples, most of them were GII/4, while sapovirus GI/2 was detected in one sample. Associations between the presence of human calicivirus and clinical and epidemiological data revealed that diarrhea occurred with a seasonal pattern, and that children hospitalized due to human calicivirus disease scored an average of 13 +/- 3.2 (SD) points on the Vesikari scale, which corresponded to severe episodes. These results highlight that human caliciviruses, by themselves, are enteropathogens of acute severe diarrhea among young Mexican children requiring hospitalization and that their detection is important in order to reduce the diagnosis gap.