SUMMER PESTS:Common food poisoning bacteria have continued to thrive this summer, despite the bad weather.

To date this year notified cases of illness through infection with salmonella, campylobacter or E.coli variant O157:H7 are similar to 2006 figures, according to provisional data from the Health Protection Surveillance Centre (HPSC).

Salmonella can cause diarrhoea, fever and abdominal cramps in humans, and infections tend to peak in warmer months of the year, according to Dr Paul McKeown, consultant in public health medicine with the HPSC.

"It's probable that overall temperatures affect it, including the temperatures at which food is stored," he said, noting that in summer people tend to eat more salads and improperly cooked eggs and barbequed meat and poultry, which could harbour the bug.

A recent outbreak of salmonella in north Kerry left at least 30 people ill and the Food Safety Authority of Ireland has warned restaurants and catering businesses to be particularly vigilant during summer months.

"A salmonella bacterium reproduces every 20 minutes, so by exponential growth, one becomes hundreds of thousands within 24 hours," noted the HPSC's Dr McKeown, adding that a dose of 1,000 bacteria could cause illness in susceptible people like babies and the elderly.

"Then in summer you have more food that is more likely to become contaminated, and a greater opportunity for it to be spread."

However the rain clouds that banished notions of barbeques this summer have had no silver lining of reduced salmonella-related tummy upsets. By early August, 242 cases had been flagged to the HPSC, compared with 206 for the same period last year, although Dr McKeown said he believed many more cases were not notified. "Realistically there may be 2,000 cases of salmonella each year in Ireland," he estimated.

He also noted a longer-term trend of salmonella poisoning falling in Ireland and across Europe since the 1990s, thanks to improved hygiene and control measures.

Meanwhile this year, human infections of campylobacter, a stomach bug associated with poultry, jumped to 1,158 notified cases to early August, up 96 on the corresponding tally last year. Again, Dr McKeown believed this to be an underestimate, estimating that Ireland could see 4,000 to 6,000 cases each year, with a peak in early summer. "Most chicken that's sold will have campylobacter on it," he noted.

Thorough cooking reduces the risk of illness from salmonella and campylobacter, and also the E.coli variant O157, or so-called "burger bug". But the E.coli variant is hardy and live bugs can hang around.

As few as 10 bacterial cells can cause illness in humans, often resulting in severe bloody diarrhoea and abdominal cramps, according to Dr McKeown.

"There's increasing evidence that [E.coli variant O157] can survive dried on metal surfaces for up to a month," he said.

Ireland tends to see most human illness from E.coli O157 in the late summer and early autumn.

By early August 64 cases had been notified here, down 17 on last year, and recently the bug was found in the water supply at the country's largest psychiatric hospital, St Stephen's hospital in Glanmire. Overseas, an outbreak this month in Paisley, Scotland, left one woman dead and several seriously ill.

The bacterium, which can live harmlessly in the guts of cattle, is acutely dependent on weather and can enter water supplies through contaminated agricultural runoff, noted Dr McKeown.

"Increasingly our outbreaks are water-borne, associated with contaminated wells and local water schemes," he said.