Clarke and Anderson (1979) worked to identify whether the Papanicolaou (Pap)
smear was an effective screening procedure for invasive cervical cancer. They conducted
a case-control study in the city of Toronto. Interviewing the subjects helped
identify the risk factors for cervical cancer. Higher education, higher age, lower annual
income, and unemployment contributed to higher relative risk of cervical cancer
in those who failed to have a Pap smear. Pap smear was considered to be less effective
in those with adenocarcinoma because it arises from the mucous glands located in the
endocervix in contrast to the squamous cell carcinoma that occurs at the squamocolumnar
junction. The researchers concluded that “the Pap smear itself has no preventive
value, and there must be appropriate follow-up and treatment of abnormal
smears.”
In 1976 an outbreak occurred as a result of an unknown agent that resulted in the
hospitalization of 147 patients and 29 deaths. Patients all had signs and symptoms of
pneumonia and a common history of attending the American Legion Convention at a
Philadelphia hotel. During the epidemiological investigation, clinical, epidemiological,
and laboratory criteria were clearly defined to identify the place, person, and time factors
and cause of the disease. Clinical criteria included cough, fever, and signs of pneumonia
in chest x-rays. Epidemiological criteria included patient attendance at the
American Legion Convention in the period from July 21 to 24, 1976, in Philadelphia. A
person was considered seropositive if he or she had a titer of 1:128 or greater by indirect
fluorescent antibody assay used to detect unknown gram-negative microorganisms. The well-defined criteria, preparation of a quality survey questionnaire, interviewing skills,
the ability to conduct a multistate study, systematic tracking of data, microbiological assistance,
and resources for autopsy led to the study’s successful conclusions. The newly
identified pathogen was named Legionella pneumophila, with the signs and symptoms
caused by it grouped under “Legionnaires’ disease.” Although the source was not identified,
it was concluded that the pathogen was airborne and that air conditioners contributed
to its spread. This is typical of an epidemiological investigation that led to the
discovery of a previously unknown pathogen (Fraser et al., 1977).