Chlamydia trachomatis antigens were detected in populations with the following infection prevalences: 26.5% (36 of 136) of men and 27.7% (48 of 173) of women attending a sexually transmitted disease clinic, 16.3% (53 of 324) of women attending a Planned Parenthood clinic, and 3.4% (4 of 117) of an obstetrics and gynecologic practice. Compared with cell culture of the combined female cervical specimens (15.8% prevalence), the respective sensitivities of Chlamydiazyme (Abbott Laboratories, North Chicago, Illinois) and Microtrak (Syva, Palo Alto, California) were 98.3% and 87.9%, specificities were 97.5% and 98.4%, positive predictive values were 87.7% and 92.7%, and negative predictive values were 99.7% and 97.5%. Both assays were 70.0% sensitive with male urethral specimens, and the other parameters of performance ranged between 84.0% and 97.2%. The antigen detection assays, compared with culture, performed equally well in subjects without or with clinical signs.

Recurrences of typhoid fever are uncommon, and the recent literature is disappointingly uninformative about them. Despite his vast experience of the disease, Bretonneau (1829) reports that he had never seen a recurrence. Eichhorst (1888) states that of 666 consecutive cases of typhoid fever in Zurich between 1884 and 1886 twenty-eight gave a history of a previous attack; he observes that the severity of the second attack was independent of that of its predecessor, and that the mortality rates of first and second attacks were about equal; the average interval between attacks was about 10 years, and in only one patient was it less than a year. Curschmann (1902) states that the incidence of second attacks in 1888 patients in the Hamburg epidemic of 1887 was 24 %, and emphasizes that clinical records of the first attacks were often available for verification. He quotes other series with 18-2-2 % of second attacks. His general observations agree with those of Eichhorst. Sawyer (1914) reports that of 93 victims of an explosive outbreak oftyphoid fever in the United States 14 patients had experienced a previous attack. Gay (1918) reviews the literature and quotes numerous estimates of the frequency of recurrences, almost all based on patients' past histories.In general, these estimates vary from 1 to 4 %, but are as high as 15 % when the character of the outbreak suggests a large infecting dose. He states that second attacks are usually less severe than first attacks, and that recurrences usually occur in epidemics. Many of the estimates quoted by Gay are open to serious question as they were made at a time when the diagnosis of typhoid fever could not have been confirmed bacteriologically or serologically, and typhoid must often have been confused with paratyphoid and even with other continued fevers.Numerous authors (Dowling, 1948;Kolmer & Tuft, 1941;Rolleston & Ronaldson, 1940;Stuart & Pullen, 1950;Top, 1947;Zinsser & Bayne-Jones, 1939) agree generally with Gay and give no new figures. The general impression conveyed by the literature is that an attack of typhoid fever confers a considerable degree of immunity but that recurrences occasionally take place.Repeated exposure to infection by Salmonella typhi cannot be common in modern civilized communities, and this must greatly restrict the incidence of second attacks irrespective of the degree of immunity conferred by one attack. Two outbreaks of typhoid fever have recently occurred in the same community within a period of .5 months thus exposing a large number of individuals to the risk of infection on two occasions; several contracted typhoid fever twice. This unusual event forms the basis of the present report.