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Vibrio cholerae can shift to a "rugose" colonial morphology associated with expression of an amorphous exopolysaccharide that promotes cell aggregation. Flow cytometric studies indicated that up to 3% of particles in rugose cultures represented aggregates of >5 bacterial cells. Rugose variants of our test strains displayed resistance to killing by chlorine, with viable cells persisting for >30 min in 2 mg/L free chlorine; strains also showed resistance to killing by complement-mediated serum bactericidal activity. Six volunteers fed 10(6) cfu of a rugose variant of V. cholerae O1 El Tor Inaba N16961 developed symptoms typical of cholera, with a mean diarrheal stool volume of 2.2 L (range, 1.4-4.3). Isolates recovered from the stool of infected volunteers retained the rugose phenotype. The data suggest that rugose strains cause human disease. The role of these strains in the epidemiology of cholera remains to be determined.

To determine whether rhinovirus infection induced a systemic cellular immune response in humans, specific antigen-stimulated blastogenesis, natural killer cell activity, and mitogen-stimulated production of interleukin-2 and interferon-gamma by peripheral blood mononuclear cells (PBMC) were quantified during experimental rhinovirus infection of normal volunteers. Phytohemagglutinin-stimulated interleukin-2 production by PBMC collected on day 5 after rhinovirus inoculation was increased fourfold compared with production by PBMC collected before rhinovirus challenge (P less than .05); phytohemagglutinin-stimulated interferon-gamma production was doubled (P less than .05). An inverse relationship was observed between the increase in interleukin-2 production and both nasal mucus production (P less than .02) and the number of days virus was cultured from nasal washings (P less than .02). Natural killer cell-mediated cytotoxicity of PBMC collected on day 5 after rhinovirus challenge was also increased (P less than .01) compared with preinfection levels, as was specific antigen-stimulated blastogenesis on day 21 (P less than .05). The extent of blastogenic response correlated directly with both mucus production (P less than .05) and the number of days virus was cultured from nasal washings (P less than .05). These observations are consistent with the hypothesis that rhinovirus infection results in activation of a systemic cellular immune response.