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In recent years there has been growing concern over the potential spread of antimicrobial resistance from the use of antibiotics in animals to humans and that they may play a significant role in causing resistance in man.
However, much of the views regarding antimicrobial resistance transfer from animals to man is speculative and it is difficult to obtain finite information of the actual risks. However, it does not stop the lay press expressing opinions of the quantity and a figure of up to 70% has been promulgated. Even in more sophisticated reports (BuRO, 2010) the Bureau of Risk Assessment and Research Programming in a report to the Dutch Government stated, “There are no hard evidence on the actual importance of transfer of resistance from the animal to the human sector but a rough estimate is that 33-50% of the resistance observed in infectious agents for humans, comes from the agricultural sector.”
It was the purpose of this paper to evaluate the potential risk of the transmission of infections from pigs to man either directly or via pig meat using an epidemiological basis. This could then be compared with the incidence of diseases in man caused mainly by bacteria and are likely to be treated with antibiotics.
A list of human bacterial infections and their incidence (mainly US data) are summarised and the potential associations with swine identified. Of the 49 infectious agents reported, potentially only nine are pig associated (approximately 18%) but they may also involve other animal species. A further bacterium, Streptococcus suis is also potentially transmissible to man from pigs, but usually affects farm workers or persons involved in the meat trade.
The major bacterial infections that are potentially associated with pig transmission (S. aureus (MRSA CC398), S. suis, B. anthracis, C. perfringens, C. difficile, A. baumannii, E. coli, Salmonella spp., C. coli, Enterococcus spp., Y. enterocolitica) were examined further and their impact regarding infection, disease, mortality and resistance transfer further assessed.
Data evaluation showed that pigs could be accountable for infections in man, especially personnel working directly with pigs. Regarding the general public, the figure was much lower at 0.0031% on a population basis, which is equivalent to 3.1 people in every 100,000. Human infections occur and are treated with antibiotics in approximately 16.34% of cases on a population basis, or 16,340people/100,000. Therefore pigs cause 0.019% of human cases and if all infections were resistant to antimicrobials this would be the contribution of resistance transmission. If the concern was just for ‘critical use’ antibiotics the figure would be as low as 0.00034% if a figure of 2% resistance is used.
In conclusion, this is the reason why antimicrobial resistance transfer to the general human population from pigs can be considered of minor importance in comparison with the direct use of antimicrobials in man by doctors in the community and in hospitals.
David G S Burch. Why is antimicrobial resistance in pigs not so important for public health?. SIPAS, 2012.