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Pulmonary tuberculosis in the middle aged and elderly male is clearly still a disease
to be reckoned with.
Public health measures vigorously pursued have reduced the risks of infection for
children and young adults but they have had less effect in present circumstances in
preventing progressive disease in older men.
Therapeutic measures too are far more successful in the first half of life than later.
At the end of this report I have set out statistical tables as measures of the various
aspects of infection, survival, etc., and these help to clarify the general picture as well
as serving for a comparative secular record. But it must be remembered in studying
these that they suffer certain shortcomings. Most tuberculosis statistics are calculated
from information provided by others and this is not always complete or absolutely
accurate. Enthusiasm for notification and even criteria for notification vary from district
to district. The figures given for various groups of people or districts may represent
a variable sample of the persons or areas. Too high a proportion (26 per cent. in 1955)
of fatal cases were certified as having died of tuberculosis but had not been notified
during life. Tuberculosis recorded as discovered among contacts and among persons
submitting to mass X-ray does not include cases that must exist among the contacts
not examined and the public not accepting X-ray examination. Not all known cases
are notified or figure on chest clinic registers. Fatal cases are not representative of tuberculous
persons as a whole—they are derived predominantly from those with less
natural resistance and are likely to include more of those who do not co-operate with
their physicians in treatment.
All the tables and graphs provided should be carefully studied in the light of the
appropriate paragraphs of the report to which they relate, when they will be found
to serve as very valuable guides.
Epidemiology of tuberculosis in London
Epidemiology
In the natural history of tuberculosis nowadays infection from a human source is by far
the commonest cause. Even a recent outbreak of tuberculosis among monkeys at the
London Zoo was attributed to such a source. Pasteurisation of milk has made bovine
type tuberculosis uncommon. Nine out of ten newly notified cases are pulmonary.
One of every three of these is found to be excreting tubercle bacilli and this represents
a measure of the degree of infectivity of unrecognised cases existing in the population.
Within a few months of treatment the majority of new cases become much less infective
or even non-infective, so that the unrecognised case is individually a more serious
public health menace than the case known and under treatment.
Searching out undiscovered lung cases is therefore the keystone in tuberculosis
control.
There is evidence that once infected, many patients are unable completely to heal
the diseased areas in the body and that these may persist as foci in which subsequent
relapse can occur even many years after apparent healing of the disease has occurred.
There is also some evidence that among adults, renewed exposure to intense infection
may act as a stimulus to breakdown of an old arrested lung lesion. Other precipitant
causes of relapse include inadequate nutrition, continued excessive physical exertion
and prolonged or deep emotional disturbances.
As infection and disease in children and young adults diminishes, so in due course
of time, there should be fewer older persons with lesions in a state of liability to breakdown.
Only a small proportion of the persons who are infected with tubercle bacilli show
signs of ill health. Tuberculin skin tests reveal the persons who have been infected,
while annual notifications and clinic registers provide a measure of those in whom
infection has progressed to disease. The highest pulmonary notification rate (1.82 per
27