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Epidemiology has features that resemble those of the traditional liberal arts. This makes it fit both for inclusion in an undergraduate curriculum and as an example in medical school of the continuing value of a liberal education. As a "low-technology" science, epidemiology is readily accessible to nonspecialists. Because it is useful for taking a first look at a new problem, it is applicable to a broad range of interesting phenomena. Furthermore, it emphasizes method rather than arcane knowledge and illustrates the approaches to problems and the kinds of thinking that a liberal education should cultivate: the scientific method, analogic thinking, deductive reasoning, problem solving within constraints, and concern for aesthetic values.

An explosive, common-source outbreak of pneumonia caused by a previously unrecognized bacterium affected primarily persons attending an American Legion convention in Philadelphia in July, 1976. Twenty-nine of 182 cases were fatal. Spread of the bacterium appeared to be air borne. The source of the bacterium was not found, but epidemiologic analysis suggested that exposure may have occurred in the lobby of the headquarters hotel or in the area immediately surrounding the hotel. Person-to-person spread seemed not to have occurred. Many hotel employees appeared to be immune, suggesting that the agent may have been present in the vicinity, perhaps intermittently, for two or more years.

To identify the etiologic agent of Legionnaire's disease, we examined patients' serum and tissue specimens in a search for toxins, bacteria, fungi, chlamydiae, rickettsiae and viruses. From the lungs of four of six patients we isolated a gram-negative, non-acid-fast bacillus in guinea pigs. The bacillus could be transferred to yolk sacs of embryonated eggs. Classification of this organism is incomplete. We used yolk-sac cultures of the bacillus as antigen to survey suspected serum specimens, employing antihuman-globulin fluorescent antibody. When compared to controls, specimens from 101 to 111 patients meeting clinical criteria of Legionnaires' disease showed diagnostic increases in antibody titers. Diagnostic increases were also found in 54 recent sporadic cases of severe pneumonia and, retrospectively, in stored serum from most patients in two other previously unsolved outbreaks of respiratory disease. We conclude that Legionnaires' disease is caused by a gram-negative bacterium that may be responsible for widespread infection.

Using decision analysis, we estimated the benefits, risks and costs of routine childhood immunization against pertussis. Without an immunization program, we predict that there would be a 71-fold increase in cases and an almost fourfold increase in deaths (2.0 to 7.6) per cohort of one million children. With a vaccination program, we predict 0.1 case of encephalitis associated with pertussis and five cases of post-vaccination encephalitis; without a program, there would be only 2.3 cases of encephalitis associated with pertussis. Community vaccination would reduce by 61 per cent the costs related to pertussis. Our analysis supports continuation of vaccination in routine childhood immunization programs, but suggests the need for more reliable data on complications from the vaccine, further study of the epidemiology of pertussis and development of a less toxic vaccine.

In February, 1976, a Peace Corps worker returned to the United States from Sierra Leone with an undiagnosed illness later recognized as Lassa fever. To assess the risk of transmission and to contain a potential outbreak, we identified 552 contacts as having had exposure to the patient before the start of strict isolation procedures, and maintained intensive surveillance on these contacts for 21 days. At the end of the surveillance period, no illness had developed in contacts. One month later, a serologic survey among 29 of the contacts judged to be at high risk gave no evidence of infection. In response to the importation of this communicable and highly fatal disease, procedures for the isolation of the patient, the identification, surveillance and management of contacts and the handling of laboratory specimens were developed and implemented. These procedures could be adapted to future introductions of highly contagious diseases.

To determine the risk of severe Haemophilus influenzae illness among household contacts of patients with H. influenzae meningitis, we studied prospective data obtained in 19 states from January 1, 1977, to June 30, 1978. H. influenzae meningitis was reported in 1403 patients, and 1147 (82 per cent) of the exposed families were investigated for the occurrence of H. influenzae disease within 30 days after its onset in the index patient. During this interval, nine of 1687 household contacts (0.5 per cent) under the age of six years had systemic disease confirmed to be caused by H. influenzae Type b. The risk in children less than one year of age was 6 per cent, and the risk in those less than four years of age was 2.1 per cent. None of 2624 contacts above the age of five was affected. In the 30 days after onset of meningitis, the risk of this infection alone, aside from other types of serious H. influenzae disease, is 585 times greater in household contacts than the age-adjusted risk in the general population. The risk of H. influenzae disease in household contacts under six years of age is similar to the risk of secondary meningococcal disease in all household contacts--indicating a need for effective antimicrobial prophylaxis.

To determine the risk factors associated with toxic-shock syndrome (TSS) in menstruating women, we conducted a retrospective telephone study of 52 cases and 52 age-matched and sex-matched controls. Fifty-two cases and 44 controls used tampons (P < 0.02). Moreover, in case-control pairs in which both women used tampons, cases were more likely than controls to use tampons throughout menstruation (42 of 44 vs. 34 of 44, respectively; P < 0.05). There were no significant differences in brand of tampon used, degree of absorbency specified on label, frequency of tampon change, type of contraceptive used, frequency of sexual intercourse, or sexual intercourse during menstruation. Fourteen of 44 cases had one or more definite or probable recurrences during a subsequent menstrual period. In a separate study, Staphylococcus aureus was isolated from 62 of 64 women with TSS and from seven of 71 vaginal cultures obtained from healthy controls (P < 0.001).

Trials of pneumococcal vaccine in healthy young adult populations suggest 75 to 95 per cent type-specific efficacy. Trials have not been done, however, in groups for which pneumococcal vaccine is currently recommended in the United States. To assess efficacy in the immunocompromised groups now receiving the vaccine, we compared serotypes of 35 isolates of Streptococcus pneumoniae isolated from blood or cerebrospinal fluid one month or longer after the patient had received commercially available pneumococcal vaccine with serotypes of 392 isolates from unvaccinated persons surveyed in a study of the nationwide distribution of pneumococcal serotypes. Proportions of infections with vaccine serotypes were unexpectedly similar. An alternative approach to estimation of vaccine efficacy suggested an average efficacy of 36 per cent in persons of all ages. The estimated efficacy was lowest in children two to 10 years old (less than or equal to 0 per cent) and in persons with preexisting diseases that are thought to predispose to pneumococcal disease (less than or equal to 0 per cent), and highest in the group over 10 years old (60 per cent). The possibility that efficacy is low in high-risk, immunocompromised populations makes it important to evaluate clinical efficacy and not just serum antibody responses in such groups.