CDC History of Tuberculosis Control - Medical and Public Health ...

TB; and d) there was also a suggestion that
social stress increased the risk of
developing TB.
A major purpose of the Muscogee County
(GA) Tuberculosis Study, started in 1946, was
to evaluate the role of mass chest x-ray surveys
in TB control. The prospectus and a description
of the coverage of the survey and prevalence
of TB were included in the first two
papers published on this study. Calculation of
participation rates was made possible by the
population denominator provided by a private
census. Basic factors associated with participation
and the prevalence among participants
were described, as well as reasons for not
taking part in the survey. Subsequent papers,
building on this foundation, were able to
provide information on the incidence of TB
among tuberculin reactors and the risks of
reactivation among persons with inactive TB,
information that has been used to the present
time.
The first report of the BCG trials in Muscogee
County and Russell County (AL) appeared in
1951. The school children vaccinated in 1947
were retested 6 months later, and many controls
and vaccinees were tested with tuberculin
again in 1950. Both groups had had less than 5mm
induration to the 100-TU dose of PPD
tuberculin in 1947. Although 46% of the
vaccinees had 5 or more mm of induration to
5 TU of PPD-tuberculin 6 months later, only
24% of them had reactions this large in 1950;
at that time, only 3% of controls had similar
reactions. Subsequent follow-up of persons in
these trials produced findings that were completely
unexpected at the time of their initiation.
In contrast to the belief that most TB
occurred very shortly after infection and that
those who survived this short-term risk were
relatively safe thereafter, approximately 80%
of TB developed among the initially positive
reactors who continued to be at risk. This
finding dashed an early hope, namely that the
source of a new case of TB ought to be readily
found among recent contacts. An unpublished
TB Control at the Millennium
50
finding involved the first 56 cases among
survey participants who did not have a known
case in the household. Some 13,000 possible
contacts were identified (relatives, friends,
workers in the same factory, school mates,
etc.). Approximately 11,000 were examined,
with the identification of only one possible
but unlikely source case. The facts that so
little TB developed among nonreactors (those
eligible for vaccination) and that BCG appeared
to cause harm among school children
and to afford very little protection to older
persons were major considerations in the
hesitancy to advise BCG vaccination in the
United States. Over a 23-year period, there
were slightly but significantly more cancer
cases among vaccinees than controls, most
markedly for tumors of the lymphoid tissues.
Many other studies were carried out by the
Field Studies Section during this period.
There were numerous reports relevant to mass
chest x-ray surveys, then in their heyday,
dealing with topics such as x-ray generators,
fluorescent screens, films, protection of personnel,
and the feasibility of taking photofluorograms
without having participants disrobe.
The development of standardized fungal
antigens, notably histoplasmin, was also an
important endeavor. Finally, and far from
least important, was the publication of Carroll
Palmer’s ideas for research that could be done
in conjunction with the mass tuberculin
testing and BCG vaccination then underway
in the International Tuberculosis Campaign.
(Editor’s note: Dr. George Comstock conducted
the trials in Georgia from 1946 to 1955.
He continued to make major contributions to
the knowledge of TB and measures to prevent
the development of TB. After retirement from
the PHS he became the Alumni Centennial
Professor of Epidemiology at Johns Hopkins
University. Dr. David Sencer, a medical
officer, was then assigned to Georgia to continue
Dr. Comstock’s work. He subsequently
rose through the CDC ranks to become the
Director of CDC, serving from 1966 to 1977.)