Capsular and 'O' serotype determinants of bacteroides fragilis.

Forty-one strains of Bacteroides fragilis, 20 strains of other Bacteroides species and 14 strains of other genera were examined by the indirect immunofluorescent assay (IFA) using anticapsular serum. The sixty-one Bacteroides strains were 'O' serotyped by direct agglutination tests using absorbed antisera raised against 23 strains, each with a different 'O' antigenic determinant. All 41 B. fragilis strains tested were positive by IFA with the anticapsular serum, but apart from one strain of B. distasonis, none of the remaining 19 strains of other bacteroides, i.e. B. thetaiotaomicron, B. distasonis, B. vulgatus, B. ovatus, B. melaninogenicus group and B. ureolyticus, and none of the 14 other bacterial species examined were positive. The majority of strains of saccharolytic bacteroides tested reacted with one of the 23 'O' antisera and were designated as a specific 'O' serotype; a few Bacteroides strains had multiple agglutination reactions indicating the presence of multiple antigenic determinants. All 'O' serotypes gave positive IFA tests with their homologous 'O' antisera. Common capsular determinants and 'O' antigenic determinants appear to exist on the same strains of B. fragilis. Serological typing of B. fragilis and related species would be useful in epidemiological studies.

Phase specific analysis of herpes zoster associated pain data: a new statistical approach.

Herpes zoster or shingles is a frequent occurrence in both elderly individuals and immunocompromised hosts. The pain associated with herpes zoster is the most debilitating complication of the disease. It can be described as acute pain and post-herpetic neuralgia or zoster associated pain (ZAP). The latter definition encompasses pain from the onset of disease through its resolution and provides a convenient analytic tool for evaluation of antiviral therapy. A heuristic examination of ZAP historical data suggests the existence of three phases of pain resolution: the acute, subacute and chronic phases. The subacute and chronic phases comprise the post-herpetic neuralgia (PHN) stage. Common analytic methods, such as a Kaplan-Meier survival function or a Cox's model, have been used to assess the pain. However, such approaches do not adequately allow for phase comparison. Notably, in the clinical trial setting the comparison of specific treatment effects on the latter stages of pain are of the greatest medical relevance since this is the most debilitating phase of the illness. In order to incorporate the phase-specific information in the modelling of time to cessation of ZAP, we assumed the hazard function was a stepwise constant. Utilizing the full likelihood function, we obtained the maximum likelihood estimate for the transition times (that is, change-points), and other parameters of medical importance. The standard error of the change-point estimates were obtained through a bootstrapping method. The asymptotic properties of the parameter estimates are also discussed. Hence, the rates of pain resolution across all phases can be examined in order to precisely define the existence of multiple phases. In addition, the covariates effect can be examined across phases and populations, thereby allowing us to translate potential efficacy of a standard therapy to different populations. These results can be utilized in the design of clinical trials or in targeting the outcome for a specific phase while controlling for the effect of other variables.