"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". 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. In contrast, deaths from tuberculosis from other causes number 7752 over the period 1972 - 1981. 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". "For the 5 years 1978 - 1982, only 4 of 99 cases of brucellosis were probably caused by milk".

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.

In 1981, 21 outbreaks from consumption of unpasteurised milk were reported with 294 people affected and in 1982, 18 outbreaks with approximately 612 people suffering. 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". 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". For example, in one report from this Centre, unpasteurised milk was the "suggested" vehicle in 21 outbreaks of salmonellosis in 1982 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.

"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. "Part of this increase is almost certainly spurious due to more interest in the disease, better and more available laboratory facilities and more improved reporting but there has also been a real increase related to changing patterns of food production, processing, distribution and consumption". Salmonellosis does not appear to have been a common disease in England and Wales in the 1930's - when much more unpasteurised milk was consumed than is now. Only 38 incidents were reported from all causes between 1936 and 1940 compared to 9461 in 1982.

In the period 1950 - 1982 there were 172 outbreaks attributed to untreated milk and 6 deaths, which is only a small proportion of the total numbers over that period. In 1982 salmonellosis attributed to untreated milk affected 412 people, only 3.2% of the total number of 12,684 who were affected from all causes. During the period 1950 - 1980 this figure was only approximately 1%. When considered in terms of 'incidents' of food poisoning, less than 3% of the total for 1982 were conclusively linked to untreated milk .

Over the 31 years from 1951 - 1982 only 6 deaths were attributed to infections from untreated milk. Yet in one year alone, 1982, there were 67 deaths from other types of bacterial food poisoning.

"Infection from Pasteurised Milk"

Contrary to popular belief, contamination with pathogens can occur in pasteurised milk. For example, 3,350 people were affected in two outbreaks of Campylobacter infection , and salmonella outbreaks attributed to pasteurised milk, dried and tinned milks, have also occurred. Other types of infection have been linked with pasteurised milk. For example, in 1982 in the United States there was a multi-state outbreak of a gastrointestinal infection (Yersinia enterocolictica) transmitted by pasteurised milk. Reported cases number 172 but estimates suggested approximately 800 individuals may have been ill. This was despite the fact that "standards for adequate pasteurisation had been met or exceeded throughout the period when contamination had occurred".