Infectious diarrhea from all causes is a major cause of morbidity and mortality among international travelers, including those who frequent wilderness areas. It would be wonderful if there was a vaccine against one or more of the infectious agents, which are commonly viruses, bacteria, and protozoa. Approximately a year ago, there was a publication in the journal Lancet (2008 Jun 14;371[9629]:2019-25) entitled “Use of a patch containing heat-labile toxin from Escherichia coli against travellers’ diarrhoea: a phase II, randomised, double-blind, placebo-controlled field trial” by SA Frech and colleagues.
To summarize what was published, it was noted that enterotoxigenic E. coli (ETEC) is a significant cause of diarrhea. These investigators were interested in evaluating the safety and efficacy of a vaccine-containing skin patch that delivered a heat-labile (e.g., sensitive to heat) toxin from ETEC.
To look at the issue, healthy adults aged 18-64 years were chosen who planned to travel to Mexico or Guatemala. They were vaccinated, utilizing patches, prior to travel. The method was to place two patches 2 to 3 weeks apart. The patches either contained the heat-labile toxin or placebo. The study individuals keep a “diarrhea diary and if they were stricken, yielded a sample to the laboratory for examination to attempt to determine the precise cause of the diarrhea.
When diarrhea struck, it was graded by the number of loose stools in 24 hours: mild diarrea (three stools), moderate (four to five), and severe (at least six). Of the approximately 200 enrollees who were given patches, 178 received two vaccinations and traveled. Twenty-four (22%) of 111 placebo recipients had diarrhea, of whom 11 (10%) had ETEC diarrhea.
The results were encouraging. The vaccine was safe and provoked an immune response. The patch recipients were protected against moderate-to-severe diarrhea and severe diarrhea. Patch recipients who became ill had shorter episodes of diarrhea with fewer loose stools than did patients with diarrhea who had received only placebo.
There is much about this study to provoke encouragement. First, it appears that the antigen used in the vaccine is effective. Second, administering a vaccine by patch eliminates the needle stick(s) associated with most other immunizations. Given the enormous distribution of patients with diarrhea, it would be marvelous to be able to apply immunization techniques to diminish the disease burden.
Future studies will no doubt look to refine the dose, define extenuating circumstances where this immunization would not be expected to work, and extend the development process to attempt to mitigate other germs, such as Campylobacter, norovirus, and perhaps even Giardia lamblia. If we could create a “multivalent” vaccine, that would be most useful.
