Clostridium tetani Tetanus toxoid is now administered routinely to most children in the United States. Hence, cases of tetanus in the United States may occur in the elderly, who may not have been immunized. The elderly seem to have a blunted response to booster doses of tetanus toxoid; this problem with efficacy in a portion of the population probably does not call for development of a new vaccine.

The Chlamydia trachomatis species contains various strains that are the etiologic agents of lymphogranuloma venereum (LGV), trachoma, and various other syndromes. There are at least 15 serotypes of C. trachomatis: three are associated with LGV and 12 are considered trachoma strains, although the symptoms they produce range from acute and chronic eye disease, urethritis in males, and genital tract infection in females, to acute ocular and respiratory tract infections in newborns and young infants (Grayston and Wang, 1978). C. trachomatis is now considered a major cause of sexually transmitted disease (e.g., mucopurulent cervicitis).

C. trachomatis is not a suitable candidate for vaccine control at this time for both biological and public health reasons (NIAID, 1984). There is little evidence of natural immunity. Results from trials with an inactivated vaccine suggest that chronic eye disease with pannus formation may result from heterotypic infection: eye disease was accentuated in vaccine recipients who later became infected with another serotype (Craighead, 1975). Field studies in Taiwan and India with multiple doses of an inactivated vaccine failed to show long-term protection (Grayston and Wang, 1978).

The number of genital and neonatal infections caused by C. trachomatis strains probably could be reduced substantially by standard public health measures, including contact tracing. Efforts also are underway to modify some antibiotic treatment protocols, i.e., for gonorrhea to ensure killing of chlamydiae which are often isolated either alone or with gonococci from cultures of patients with urethritis (Bowie and Holmes, 1979).

The E. histolytica ameba frequently is found living as a commensal in the lumen of the human large intestine, producing large numbers of infective cysts that are transmitted by the fecal-oral route. It also may produce invasive amebiasis, however, with symptoms ranging from mild dysentery to life-threatening fulminant, hemorrhagic infection with high fever. Liver invasion with abscess formation also may occur.

While amebiasis is not common in the U.S., loci exist in both institutional and non-institutional settings (Krogstad et al., 1978). Prevalence rates among male homosexuals may range from 20 to 30 percent in some large cities (Kean, 1976, 1981; Phillips et al., 1981; Pomerantz et al., 1980).