A study of shigellosis in Tasmania

In a recent publication, Tasmania was designated as an area of moderate or unknown status in regard to the overall problem of diarrhoea (DuPont and Pickering, 1980). This impression seems to be at least partly the fault of Tasmania itself. For example, between the years 1976 to 1983, only eleven cases of Shigella infection were reported, an average of 1.6 cases per year. This not only made it appear that Tasmania had a very low incidence of this infection in comparison with the rest of Australia, but also in fact, with most of the rest of the world. Considering that Tasmania is no longer isolated from the mainland or the rest of the world, and also the fact that there is a large movement of people in both directions, including many tourists from countries with high incidence of diarrhoeal infections, it would seem very unusual to have so few cases of Shigella infections on record. There could be a number of reasons for this situation, the main ones being: (a) that dysentery (including Shigella infections) are not all being investigated and notified; (b) that it is true there is a very low incidence which in itself is interesting, and should be investigated further in order to establish, if possible, the reasons for such a fortunate situation; (c) infections do occur but for reasons unknown, are not detected, e.g. specimens are not being sent to the laboratories for investigation, or the organisms are not being isolated by the laboratories. This may involve the culture media presently available or those being used by diagnostic laboratories not always recovering or isolating the organisms. (d) The distance between the areas of collecting and the diagnostic laboratory may cause delay in the investigation. This could be significant as it is a well known fact that the Shigellae need to be plated onto culture media almost immediately; even a short delay can reduce considerably the chance of isolating the organism. Finally, there is a need to examine the possible introduction of a more rapid method to overcome the problem of delay in isolating Shigella infections combined with a more reliable method of detecting positive cases than the recovery of the organisms on culture media. It was decided to combine the investigation of the alleged lack of Shigella infections in Tasmania with an overall research project as follows: 1. Research Protocol To investigate the accuracy of presently available culture media to detect Shigella organisms using known strains and stock cultures of local strains to determine to what extent they can be recovered on available culture media, both directly and in dilution. 2. Due to the close relationship between Escherichia coil (A - D) (Alkalescens dlspar) and Shigella, this former group of organisms will also be tested against the media as for Shigella. 3. To establish if Shigella infections are being missed, due to the fact that patients with diarrhoea are not being investigated by the laboratories, the cooperation of local doctors was obtained to submit specimens from any diarrhoeal patient, even if only having mild symptoms, and provided it was suspected the diarrhoea was due to infection. Further, the co-operation of laboratories was obtained to submit diarrhoeal specimens they had found to be either positive or negative for microorganisms known to cause diarrhoea. 4. Having isolated suspected Shigella colonies, to establish which biochemical methods are most satisfactory for their rapid confirmation. 5. Due to the close relationship between Escherichiacoli and Shigella, to investigate the frequency of toxigenic E. coil and invasive E. coil by gene probe analysis in those specimens from patients with diarrhoea in which no other possible pathogens had been isolated. This has never been investigated in Tasmania. 6. To investigate the possibility of developing a more rapid and accurate technique for the identification of shigella infections in stool specimens, e.g. E.L.I.S.A. technique.