To the Editor: Keeping fish as pets, as with other animals, carries the risk of zoonotic infections. A 2000 review of bacterial zoonoses that can be acquired topically from fish commented on infection with Aeromonas hydrophila, Edwardsiella tarda, Erysipelothrix rhusiopathiae, Mycobacterium marinum, Streptococcus iniae, Vibrio vulnificus and Vibrio damsela.1 Our public health unit was recently notified of a case of Salmonella infection acquired from a fish tank.

In October 2003, a 14-month-old boy was admitted to hospital with a 2-day history of fever, vomiting and diarrhoea. Culture of three stool specimens revealed a Salmonella isolate. This was identified by serotyping (at the Institute of Medical and Veterinary Science, Adelaide, South Australia) and phage typing (at the Microbiological Diagnostic Unit, Melbourne, Victoria) as Salmonella enterica serotype Paratyphi B var Java phage type Dundee.

The child had no recent history of overseas travel or overseas visitors. Other family members were well, and their stool specimens were negative for Salmonella spp. However, the family kept a tropical fish tank, and the child’s parents reported that he would place his hands in the water to help feed the fish. Culture of water from the tank revealed a Salmonella isolate identical to that in the stool specimens.

We believe that the boy became infected after touching the water while feeding the fish. The fish tank contained red-eyed tetras, bala sharks, silver dollars and angel fish, which had been purchased from three local aquariums several years previously. None appeared sick at the time of the child’s illness.

It is important for clinicians to recognise that Salmonella infections are not always foodborne in origin. Salmonellosis is a well-known zoonosis that can be found in a variety of pets, including cats, dogs, birds, rodents and even reptiles.2 In fact, an estimated 90% of all reptiles shed Salmonella spp. in their faeces.3 Salmonella spp. have been isolated from tropical fish aquariums previously; unusual Salmonella serotypes were found in eight of 100 tropical aquariums sampled in Wales.4 Fish can excrete Salmonella without appearing unwell.5

Our patient was a 14-month-old child. In a Canadian outbreak of S. enterica serotype Paratyphi B linked to aquariums, five of seven cases were also in children aged under 10 years.5 This may reflect a combination of immature immunity and behaviour — young children may not wash their hands properly (or at all) before eating or touching their mouths.

This case highlights the importance of good handwashing at all times after contact with an aquarium, regardless of the appearance of the fish. It may also be worthwhile recommending close supervision of children under 5 years of age around aquariums.