Study investigates new salmonella strain in NZ
21 December 2001
Study investigates new salmonella strain in New Zealand
The early results of a national study into a recent outbreak of salmonella infection that caused a major increase in New Zealand cases and one death reinforce the need to follow food safety and hand hygiene advice.
The Ministry of Health study, carried out by regional public health services and the Institute of Environmental Science and Research (ESR), investigated sources of human infection with salmonella typhimurium phage type 160 (STM160), said Dr Bob Boyd, Ministry of Health Chief Public Health Safety and Regulation Advisor.
"Contact with an individual with diarrhoea in the previous month or with wild birds or their droppings, sometimes through drinking untreated water from domestic roof-collected rainwater supplies, were identified as risk factors.
"These findings, yet again, show the benefit of following food and water safety advice as well as the need for hand hygiene."
In this study, cases were over four times more likely to have had contact with another individual with diarrhoea or vomiting in the 28 days before they became ill. Salmonella is a germ that is easily spread from person to person and through food.
"Although the illness can be relatively mild, people with diarrhoea need to be especially careful about following standard hygiene recommendations. After going to the toilet they should wash their hands with soap and water for at least 10 seconds and then dry them for another 10 seconds on a clean dry cloth towel or disposable paper towel."
People who caught salmonella infection were 30 times more likely than well people to have touched wild birds within the three days before the onset of their illness. Wild birds carry STM160 and excrete the germ in their droppings.
"Care should be taken to avoid contact with wild birds or their droppings. Special care is needed when disposing of dead birds -- people should wear gloves and wash and dry their hands carefully afterwards," Dr Boyd said.
STM160 is not a new strain of salmonella internationally, but this is the first documented outbreak of it in New Zealand.
The study, carried out between April and August this year, compared people who had caught this strain of salmonella with two healthy people from the same suburb and age group. There were 117 cases investigated.
Some cases had drunk untreated water from domestic roof-collected rainwater supplies in the three days before they became ill. STM160 was found in four of the eight water supplies tested. As STM160 is carried in the gut of birds there is a risk their droppings may contaminate untreated roof water supplies. Treating water by boiling, disinfection and filtration are ways to reduce the chance of exposure to the germ.
Eating raw eggs in products like eggnog, raw cake mix or mousse was not associated with STM160 infection but still carries food safety risks and is not recommended.
People with concerns about STM160 should contact their local Public Health Officer through their District Health Board.
Contacts for further Information: Dr Greg Simmons Public Health Physician, Auckland Regional Public Health Phone (09) 623 4613 (direct dial), 025 88 4657.
Dr Craig Thornley Public Health Physician, ESR Ph (04) 914 0678 (direct dial)
or Anne-Marie Robinson, Media Advisor, Ministry of Health ph: 04-496-2067 or 025-802 622 http://www.moh.govt.nz/media.html
For extra information on reducing the public health risk from drinking roof water see the Ministry of Health's risk management plan guide for roof water sources, which can be downloaded from the Ministry's website at www.moh.govt.nz \ Publications \ Online publications \ June 2001\ Public health risk management plan guides for drinking-water supplies~ Roof water sources
What is Salmonella? Salmonella is a bacteria that can cause disease in animals and humans. The bacteria are common in nature and can cause isolated cases of disease or outbreaks.
How is the disease transmitted? The bacterium is usually transmitted by infected faeces/droppings. The bacterium can survive for a long time outside the body. Swallowing the bacterium causes infection. Food or water can become contaminated with the bacterium and lead to infection when consumed.
How many cases of STM 160 have there been in New Zealand recently? STM160 has emerged as an major source of human gastroenteritis in New Zealand over the last three years. No human cases were identified in New Zealand before 1998. One case was identified in 1998 and one in 1999 before case numbers began to increase steeply from June 2000 onward. For the year 2001 to December 14, there were 2275 cases of Salmonella infection compared with 1802 for all of 2000. STM160 was isolated in one-third of all human Salmonella cases in the year to November 2001. During November 2001, STM160 accounted for almost one-half (47 percent) of all cases.
How have sparrows contracted salmonella? Salmonella is not unusual in birds, however this current outbreak of disease in birds is unusual. Not all birds which get the illness die -- some will remain well and can excrete the bacteria for weeks, potentially infecting other animals. Large numbers of sparrow deaths in Canterbury during 2000 were attributed to STM 160 infection.
Are other animals and humans susceptible to salmonella? Yes. A wide range of animals can become infected with salmonella. Domestic cats and humans can become infected. The disease can transfer to humans through direct hand contact with bird faeces, eating food with contaminated hands, preparing food with contaminated hands, and contact with infected animals (particularly their faeces). Careful hand hygiene is recommended as a precaution.
What are the symptoms of salmonella? In humans, the symptoms usually include three-10 days of diarrhoea, headache, abdominal pain, nausea, fever and vomiting. Symptoms usually develop within two days after exposure. People experiencing prolonged symptoms should seek medical advice. In the young and elderly, symptoms can be severe and may require hospital admission. About one in every seven (15 percent) cases in the STM160 study had been admitted to hospital for their illness. In the study, 37 percent of participants were children under five years old.
Will a cat get sick if it eats infected birds? Possibly.
Who should I contact for further information? People with symptoms of salmonella infection should contact their local General Practitioner People with concerns about pets should contact their vet
What other steps should be taken to prevent STM 160 being spread by people who have had diarrhoea? Those with symptoms of diarrhoea should not handle food for others or work in the kitchen environment. Those with persisting or severe symptoms of diarrhoea should consult a doctor for diagnosis and further management. Special care should be taken with hand hygiene after changing the nappies of children with diarrhoea.
How many eggs were tested in the study and what were the findings? As part of the outbreak investigation 180 egg samples from Auckland (a total of 918 eggs) were analysed. These were the same brand and purchased from the same supermarkets as those eaten by cases reporting raw egg consumption. STM160 was not found on the surface or inside these eggs. However, other salmonella bacteria were identified on the outside of some eggs.
Is it safe to eat raw eggs then? Although no association was found between STM160 infection in the national study, eating raw eggs is not recommended. This is because other salmonella bacteria may be present on the surface of eggs and contaminate the contents of the egg when they are broken.
How can I handle eggs to ensure food safety? Cooking eggs will kill bacteria. Hands should be carefully washed and dried after handling raw eggs as germs spread by hand are the most common way of contaminating other foods eaten by your family. Eggs are perishable and should be stored in the refrigerator, cracked eggs should be thrown out.