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The source of salmonella contamination of soil on Guam.

The annual incidence of laboratory confirmed salmonellosis on the island of Guam exceeded 100 cases per 100,000 population every year from 1980 through 1989. Typically about 50% of these cases have been infants. Although food poisoning has been incriminated as the cause of salmonellosis in adults on Guam, it has been suggested that infants may more commonly be infected by some other means, possibly by contaminated soil tracked into homes on the footwear of other family members (1).

A study of soil contamination in children's playgrounds apparently supported this hypothesis and concluded that stray dogs might be responsible for the spread of Salmonella bacteria in the environment of Guam (2).

Materials and methods

If stray dogs are the most important source of the environmental contamination with Salmonella bacteria observed on Guam, then areas from which these animals are excluded should be relatively Salmonella-free. To test this hypothesis, Guam villages were surveyed to locate homes of families which did not own dogs or cats but did have an apparently dog-proof fence or wall and gates surrounding their property. A nearby unfenced property (preferably directly across the street) whose owners also did not own dogs or cats was selected for comparison. Approximately 25 gm of surface soil was collected from four corners of each property at least one meter inside the fence or property line. Sterilized wooden tongue depressor blades were used to loosen soil and transfer it to sterile plastic bags for transport to the laboratory. If the family owned a vacuum cleaner, a sample of its contents was also collected. Soil and vacuum cleaner content specimens were examined as previously described (2).


Eighteen (50%) of the soil samples collected from fenced yards were positive for Salmonella, while 22 (62%) of samples from unfenced yards were positive for Salmonella. None of the premises tested (fenced or unfenced) was free of Salmonella contamination. Seven of nine households with fenced yards used a vacuum cleaner in their home; one of these vacuums contained detectable Salmonella (fenced home no. 1, S. oranienburg). Seven of the unfenced homes also used a vacuum cleaner; again one was positive for Salmonella (unfenced home no. 5, S. java).


This study found that samples collected from unfenced yards of homes on Guam were more frequently contaminated with Salmonella bacteria than those collected from fenced yards, but the difference was not statistically significant (odds ratio = 0.64, 95% confidence interval = 0.22-1.80). These results suggest that animals other than stray dogs must also be important sources of the unusually heavy environmental contamination with Salmonella bacteria observed on Guam compared to other areas (3). The fact that no fenced yards were found to be Salmonella-free also suggests that small animals for which most fences are not an effective barrier must be contributing to this problem. All of the native birds of Guam are extinct or greatly reduced in number due to predation by an introduced snake species (4) but a recent study has shown that a small lizard (Carlia sp.) and a toad (Bufo marinus), both common in residential areas of Guam, are frequent carriers of Salmonella bacteria (5). Lizards and toads may, in fact, serve as surrogates for spreading the Salmonella serotypes carried by dogs as they have been observed stationing themselves near fresh dog stools to collect the flies that are attracted.

Fencing of yards, then, may minimize the public nuisance impact of stray dogs but cannot be depended upon to provide protection against the spread of Salmonella contamination to the home environment. This risk is emphasized by the finding of Salmonella bacteria in two of the 14 vacuum cleaners examined in this study. In both cases, the Salmonella serotype isolated from the vacuum cleaner had also been isolated from yard soil of the same house, suggesting that yards may have been the source of this contamination.


1. Haddock, R.L. and J. Malilay (1986), "A search for infant salmonellosis risk factors on Guam," Southeast Asian J. Trop. Med. Pub. Health 17:38-42.

2. Haddock, R.L. and F.A. Nocon (1986), "Salmonella contamination of soil in children's play areas on Guam," J. Environ. Health 49:158-160.

3. Haddock, R.L., C. Murray, A. Kuhmonen, G. Giammanco, M. Jegathesan, E.K. Pretrick, K.T. Goh and E. Vallone (1986), "Salmonella contamination of children's play areas: An international survey," J. Environ. Health 49:161-162.

4. Savidge, J.A. (1987), "Extinction of an island forest avifauna by an introduced snake," Ecology 68:660-668.

5. Haddock, R.L., F.A. Nocon, E.A. Santos and T.G. Taylor (1990), "Reservoirs and vehicles of Salmonella infection on Guam," Environ. Int. 16:11-16.
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Article Details
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Author:Nocon, Florencia A.
Publication:Journal of Environmental Health
Date:May 1, 1993
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