Epidemiologic aspects on antibiotic resistance

The increasing usage of antibiotics has selected for resistant bacteria. Spread of such bacteria may follow mathematical models of infectious diseases, taking into consideration the number of infectious individuals, the number of susceptible individuals, and the effective contact rate between individuals from these two groups. According to calculations of the theoretical epidemic curves, the highest incidence of individuals infected with a resistant bacterial strain is present when the prevalence of patients and carriers is approximately 20-80%. Moreover, the rapidity of the spread of an epidemic increases drastically if the total number of individuals in the exposed group increases and also if the contact rate increases. This means that precautions to stop an epidemic spread of a resistant bacterial strain in a given group of individuals should be undertaken early when the prevalence is below 20%. Efficient precautions consist of cohort isolation, decrease of the number of individuals in exposed groups by subdivision into several smaller groups, and decrease of contact rates by hygienic precautions. Examples are given where such precautions have proven efficient.