Sir.—We read with interest the article "Clostridium difficile Cytotoxin in a Pediatric Population" by Thompson et al (Journal 1983;137:271-274). They give three hypotheses for the absence of gastrointestinal (GI) symptoms in infants with fecal toxin, with one being protection by maternal antibody.
We have examined serum, from children of different ages and pregnant women, for the presence of neutralizing antibodies to C difficile cytotoxin, and we report our findings. Tests were performed by a microtiter technique used in a previous report from our laboratory.1 A broth culture of C difficile was tested for its toxin titer against Hela cells and was diluted to give 4 cytopathic units (CPUs) of toxin when added to tissue cultures. We defined 1 CPU of toxin as the amount that causes morphologic changes in greater than 90% of cells. Serum was incubated at room temperature for 30 minutes with an equal volume of