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Types of Infection carried in Milk
Fears about the risk of many diseases once associated with milk are now largely
unfounded. "By the end of the 1960's tuberculosis (TB), typhoid fever,
paratyphoid fever, bacillary dysentry, scarlet fever and staphylococcal
intoxication conveyed by milk had disappeared, brucellosis had declined" (30).
From 1951 -1960 there were 3 cases of TB (no deaths) attributed to untreated
milk and in the subsequent 20 years (1961 - 1980) no cases at all (31). In
contrast, deaths from tuberculosis from other causes number 7752 over the period
1972 - 1981 (32). In 1961 - 1980 there were only 10 cases of brucellosis
attributed to untreated milk, although as acknowledged in one report "most cases
of brucellosis are occupationally associated with cattle, and it is difficult to
prove that milk was the primary source of infection" (31). "For the 5 years 1978
- 1982, only 4 of 99 cases of brucellosis were probably caused by milk" (30).
The majority of infections attributed to milk during this period were outbreaks
of salmonella food poisoning and campylobacter infection, with a few isolated
cases of other infections. For the decade 1971 - 1980, there were 86 outbreaks
of infection attributed to untreated cow's milk with 1096 people affected (31).
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In 1981, 21 outbreaks from consumption of unpasteurised milk were reported with
294 people affected (33) and in 1982, 18 outbreaks with approximately 612 people
suffering (34). The question is whether these figures represent a true increase
in the numbers of people infected by consuming unpasteurised milk, and if so,
why, or whether they are the result of increased reporting of this type of
infection, with possibly undue blame put on milk.
The Reporting of Food Poisoning
Reporting of food poisoning can be influenced by fashion, which in recent years
appears to have become anti-Green Top. The assignment of blame to untreated milk
is often based on circumstantial evidence and other potential sources of
infection are not always investigated. "Trends in reporting (food borne disease)
may reflect changes in investigative personnel and public awareness of food
borne disease as much as actual numbers of people ill" (35). Those purveyors of
cooked meats or chickens who in the past may have received their undue share of
attention may sigh with relief whilst the focus is on milk. Sadly the reputation
of all Green Top producers, not just that of those implicated in outbreaks of
infection, has suffered as a result.
Furthermore, "in the incidents reported to the Communicable Disease Surveillance
Centre, the food vehicle of infection is only infrequently confirmed
epidemiologically or microbiologically. Therefore food items reported to be
vehicles of infection should be viewed cautiously" (36). For example, in one
report from this Centre, unpasteurised milk was the "suggested" vehicle in 21
outbreaks of salmonellosis in 1982 (36) whereas in another report published two
weeks later, the figure given was 15 and it was admitted that the causative
organism was isolated from milk, milk stocks, or both in only 10 of these
outbreaks (34).
The General Increase in Food Poisoning
The apparent increase in salmonella infections is by no means confined to those
contracted from milk - there has been a great increase from all causes (36,30).
"Part of this increase is almost certainly spurious due to more interest in the
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