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21
A public water supply unquestionably reaches a larger percentage
of the people than any other single potential disease vehicle,
but milk follows a close second. As milk is also a natural growing
medium for certain disease producing bacteria, it can be appreciated
how milk-bourne epidemics occur. In the past, outbreaks of
typhoid fever, scarlet fever, sore throats, etc. were traced to the
milk supply. Fortunately such outbreaks have become exceedingly
rare, but we occasionally have a reminder that care is still necessary.
A few years ago a sharp outbreak of para-typhoid in the west
of London and in which Acton participated was traced to contaminated
cream, and an extensive outbreak of sore throats in Brighton
was traced to an infected milk supply. At the present time the
most prominent aspect of the milk question is the prevalence of
tuberculosis in milch cows. It is generally admitted that an improvement
has been secured in the cleanliness of the milk supply.
The risk of typhoid and scarlet fever from an infected milk supply
is remote and it is possible now to feed a baby on cow's milk even
in the summer without much fear of epidemic diarrhoea. It can
be safely said that the markedly improved methods of production
and distribution in recent years made our milk supply cleaner and
safer. But whether there has been any corresponding decrease in
the frequency with which milk is infected with tubercle bacilli, it
is not possible to say with certainty. As the Committee was asked
by a Voluntary Association to pass certain resolutions, it may be
necessary to state the grounds on which this course of action is
based.
In the report of the Ministry of Agriculture for 1929, it was
stated that there were over two million cows and heifers in England
and Wales in milk, in addition to nearly 300,000 cows in calf but
not in milk and 364,763 heifers in calf. It is estimated that about
40 per cent of these are tuberculous, that is, would give a positive
tuberculin test. That does not mean, of course, that the milk. from.
40 per cent of these contains the tubercle bacilli. The figures are
important only as far as they show the magnitude of the problem.
The tuberculin test is a qualitative one and not a quantitive one;
it thus gives no indication of the degree of infection present, except
that heavily affected animals may not re-act to the test. So great
is the risk of the spread of tuberculosis in. a herd from a re-actor
to the tuberculin test that for practical purposes such re-actors are
to be regarded as infective. In view of: the high incidence of bovine
tuberculosis it would obviously be futile to recommend the
immediate elimination of all re-actors irrespective of whether or
not they are giving tuberculous milk. All the re-actors to the
tuberculin test do not give tuberculous milk, and in order to
estimate the proportion of cows which are doing so, it is important