Now wash your hands...

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A new study has found that some aquariums contain bacteria that are capable of producing serious infections in humans.

According to the results of a study by a team of microbiologists from a number of Australian academic institutions, research has shown for the first time that fish tanks can act as reservoirs for potentially dangerous multidrug-resistant strains of Salmonella capable of causing serious illness in humans, particularly young children.

The results, which have just been published in the journal Emerging Infectious Diseases, provide evidence to suggest that aquariums are a potential source of a strain of Salmonella called S. paratyphi B dT+. This bacterium causes gastroenteritis and is resistant to a number of drugs, including ampicillin, chloramphenicol, streptomycin, spectinomycin, sulfonamides and tetracycline, making it more resilient and harder to treat.

Widespread problem?The presence of Salmonella and other enteric pathogens such as Aeromonas in aquarium water has been known about for some time. The December issue of the Canadian Journal of Public Health also carried a paper investigating a link between Salmonella infections and maintaining an aquarium.

This study questioned 53 people who were suffering from a Salmonella paratyphi B infection and found that 60% of the patients had bought tropical fish, or had contact with an aquarium before becoming ill.

The scientists responsible for the study tried to trace the source of the infections and took samples from tropical fish shops and wholesalers, as well as home aquaria. They found that half of all samples contained a number of different strains of Salmonella paratyphi.

The team said that fish tanks were a risk factor in developing Salmonella, and that fishkeepers seemed unware of the potential dangers. They recommend that information be produced and distributed to pet shops and their customers to inform them of safety precautions in order to reduce contamination risks from bacterial pathogens that might be living in their aquarium water.

How big is the risk?Although these two studies have identified a potential risk, Practical Fishkeeping is not aware of a widespread problem with fishkeepers suffering from infections that are anything above the norm.

Most Salmonella infections cause a mild stomach upset that may go unreported, masking the scale of the problem from the medical profession. However, the bacteria can cause a greater risk to the very young, very old or pregnant.

In an interview with The New York Times, Dr Diane Lightfoot of the University of Wollongong told the paper that she was a fishkeeper herself and that she wouldn't wish for people to stop keeping fish:

"The world would be a terrible place without fish tanks. We're just calling on people to use common sense. Wash your hands frequently with soap and water. And when Mum's cleaning the tank, a child shouldn't play with the pebbles or sticks or splash in the water. It's easy to get infected."

Dr Colette Gaulin, who was one of the team behind the study from the Canadian Journal of Public Health, told the New York Times that the health ministry in Quebec had produced brochures and posters to educate the public on how to maintain their aquaria with the least risk to their health.

Have you suffered from lots of stomach upsets? Tell us about it on the blog.

Among the recommendations, says the New York Times, are guidelines to change a third of the water every fortnight, and to follow manufacturer's guidelines on cleaning filters. It advises against washing aquarium accessories in the kitchen or bathroom sink: "If you have no other option, then thoroughly clean and disinfect all the surfaces used with a bleach solution of four tablespoons per liter of lukewarm water. Rinse these surfaces well before reusing."

Aquaculture linkPrevious epidemiologic studies on Salmonella have linked the paratyphi B dT+ strain with aquaculture, and the fear is that the uncontrolled use of antibiotics may have been responsible for the new form of drug-resistant bacteria.

However, no molecular data has yet confirmed that the strain did derive from aquaculture, but the first reported case of SGI1-containing S. paratyphi B dT+ did come from a Singapore aquarium.

Practical Fishkeeping's fish health contributor, Dr Peter Burgess told us: "Judging from the scientific literature available to me, it seems there may be a link between tropical fish and certain antibiotic-resistant forms of salmonella. However, it isn't clear whether the use of antibiotics on ornamental fish farms has directly led to the emergence of these salmonella "super-bugs". We should, however, encourage all fish farms to minimse the use of antibiotics, to decrease the likelihood of antibiotic resistance amongst bacterial pathogens.

"Any human health risk associated with the fish-keeping hobby should be taken seriously, however we must bear in mind that fish are amongst the safest of pets to keep.

"Even the medical professionals allow aquariums in hospital wards and in doctor's and dentist's waiting rooms. As with any pet, always wash your hands after handling fish or their water."

For more details see the papers: Levings RS, Lightfoot D, Hall RM, Djordjevic SP (2006) - Aquariums as reservoirs for multidrug-resistant Salmonella Paratyphi B. Emerg Infect Dis. 2006 Mar.

Gaulin C, Vincent C, Ismal J (2005) - Sporadic infections of Salmonella Paratyphi B, var. Java associated with fish tanks. Can J Public Health. 2005 Nov-Dec ; 96(6): 471-4.