It is worth differentiating between comparative and library typing systems, as their value is different for different settings e.g. surveillance or outbreak investigation.

Comparative typing is to date the most common approach and can be used to study organisms within a defined context. An example for this approach would be the comparison of Salmonella strains from a contaminated food and disease case in a food-borne outbreak. A comparison of the two strains will show the similarity of the two strains detected and allow for conclusions about the food being the source of the outbreak. However simply typing an isolate from a human case, using the same typing technique, cannot be used to infer conclusions about the outbreak source as the results have no universal meaning.

On the other hand library typing is characterised by standardisation, high-throughput and a uniform nomenclature. This allows for meaningful interpretation of typing results in the absence of direct comparisons and for understanding typing results universally irrespective of when, where, or by whom the results were generated.Library typing has its main application in surveillance and monitoring and investigation of longer time periods but is becoming increasing available through the development of typing schemes such as MLST. Cost and benefits of library and comparative typing approaches have to be carefully considered and can vary considerably between different approaches. Such an evaluation should not only consider the monetary cost of equipment, but also the resources needed to for example train individuals in the technique.

Picture courtesy of the CDC public health image library

References:

Struelens, M.J., De Gheldre, Y., Deplano, A., 1998. Comparative and library epidemiological typing systems: outbreak investigations versus surveillance systems. Infect. Control Hosp. Epidemiol. 19:565-569. Infection Control and Hospital Epidemiology 19, 565-569.

Zadoks, R.N., Schukken, Y.H., 2006. Use of molecular epidemiology in veterinary practice. Veterinary Clinics of North America-Food Animal Practice 22, 229-+.