Improved isolation of Chlamydia trachomatis from a low-prevalence population by using polyethylene glycol.

The effect of polyethylene glycol (PEG) on the isolation of Chlamydia trachomatis was evaluated in our laboratory. Initial range-finding experiments demonstrated that the number of chlamydial inclusion bodies increased with increasing PEG concentrations. However, PEG concentrations above 10.5% became progressively more toxic to the McCoy cell monolayers. When 50 frozen clinical Chlamydia isolates were inoculated onto McCoy cell cultures with and without 7% PEG, the PEG-treated cultures produced three- to fivefold more chlamydial inclusions than cultures without PEG. This enhancement was also observed when 1,144 fresh clinical specimens from a low-prevalence population were tested. With fresh clinical specimens, PEG-treated cultures produced two- to sixfold more inclusions than standard cultures. The addition of 7% PEG to the chlamydial overlay medium significantly increased the number of inclusions in each culture, improved the sensitivity of the culture, and decreased the probability of missing a weakly positive specimen.

Impact of swine influenza vaccine on serum antibody.

Comparison of a 1976 serum survey with one of 1977 has permitted an assessment of the impact of the national swine influenza vaccine program of 1976-1977 on the antibody status of the Michigan population. Prevalence of HI influenza virus antibody in premarital sera collected in 1976 prior to the vaccine program was compared to that in similar sera collected in 1977. Overall prevalence of A/New Jersey antibody (titers greater than or equal to 1:10) in 1976 sera was 22.3%. Little antibody was detected in sera from persons less than 40 years of age and prevalence peaked at age 50. Increased antibody prevalence was found for all age groups in sera collected in 1977 following the vaccine program, and the overall prevalence was 41.6%. Only 3.5% of those under 19 years of age were vaccinated, and post-vaccine prevalence for this group was 10%. This age group, comprising about 30% of the state population, appears to have had least exposure to swine influenza virus, and may be the population segment at greatest risk of infection should strains of this antigenic composition reappear. In contrast, highest prevalence of A/Victoria antibody was found in the 15 to 19 age group, where prevalence was 52%, compared to an overall prevalence at 40%.