It’s happened again: Another food safety scare, making two in the last two weeks.

The double-whammy of the E. coli bacteria found in Hudson Foods prepackaged hamburger patties and a warning of higher risk of bacterial infection from uncooked Puget Sound shellfish has pointed up yet again how vulnerable Los Angeles-area restaurants, grocery stores and consumers are to food contamination.

“We live in a society that depends on mass-produced food, where one instance of contamination can impact the food supply for tens of thousands or even hundreds of thousands of people,” said Art Tilzer, director of consumer protection with the environmental health section of the Los Angeles County Department of Health Services. “We also live in a multicultural society that wants food from a world market. That too brings an enhanced potential for bringing in contaminated food.”

Another reason for the increased frequency of warnings: improvements in detection and reporting techniques at food-related businesses and government health regulatory agencies.

“We have much more sophisticated testing now than we did five or 10 years ago,” said Bill Marinelli, owner of Marinelli Shellfish Co., one of the state’s largest suppliers of oysters, with operations in Los Angeles and San Francisco.

The impact of the latest cases on Los Angeles-area restaurants seems to have been relatively minor. Some hamburger chains have suffered a drop in customers while some seafood restaurants, sushi bars and fish markets have either stopped serving raw oysters or are scrambling to find alternate supplies.

But the cases are bound to add to general concerns about food safety at stores and restaurants from an already uneasy public, according to Lisa Doermann, a spokeswoman for the Los Angeles chapter of the California Restaurant Association.

In a recent survey conducted by the CRA, 70 percent of restaurant operators reported that their customers are more concerned about food safety issues now than they were five years ago.

The publicity from the E. coli beef scare has no doubt contributed to this anxiety. The E. coli bacteria was discovered in meat processed at a Hudson Foods plant in Nebraska. Hudson officials said the contamination originated in one of the slaughterhouses with which it contracts; nonetheless, Hudson voluntarily recalled 25 million pounds of beef.

“We have seen a noticeable drop in customers, but I would not say it’s substantial,” said Brent Maire, general manager of Glendale-based Tommy’s World Famous Hamburgers.

Maire said he believes customers will return once the scare dies down.

“We always use fresh hamburger patties and our patrons can see them cooking on the grill, so they know we are preparing the meat properly,” Maire said.

Tommy’s also has been sending its employees to a meat-handling safety training course put on by the CRA. The course, called ServSafe, trains over 8,000 food handlers a year.

The CRA also supported a bill that passed the state Legislature last month requiring that all commercial food servers cook their meat and poultry products to at least 160 degrees Fahrenheit to kill any bacteria that may be present. Gov. Pete Wilson is expected to sign the bill this month.

Beef isn’t the only food raising safety concerns recently. While it hasn’t received much attention, the shellfish warning has had more widespread impact here in Southern California. The warning, issued by the California Department of Health Services, covers all uncooked oysters, mussels and clams from Puget Sound.

Health officials say the El Ni & #324;o weather conditions have caused the ocean waters of the Pacific Northwest to warm, leading to an increased risk of bacterial contamination in shellfish.

The bacterium, called Vibrio parahaemolyticus, has already caused five cases of illness in the Los Angeles area, according to the L.A. County Department of Health. Symptoms include diarrhea, abdominal cramps, nausea, vomiting, headache, fever and chills.

Despite the seriousness of the symptoms, this particular bacterium is generally regarded as less threatening to human health than the Vibrio vulnificus bacterium identified in Gulf Coast shellfish last year, which claimed five lives.

The state warning tells the public to cook all shellfish harvested from the Puget Sound. Typically, mussels and clams are cooked before serving. But there has been an increasing trend toward consumption of raw oysters, especially at oyster and sushi bars and seafood restaurants.

“Sushi bars and oyster bars are proliferating because of public demand. That demand is based largely on cultural factors: we have a large Asian community here in Southern California that has traditionally eaten raw sushi and raw oysters,” county health official Tilzer said.

As with many ethnic foods and customs in Southern California, the popularity of raw seafood has spread into mainstream circles.

At the Water Grill in downtown Los Angeles, for example, chef Mark Gold said he is no longer serving oysters from Puget Sound. Instead, he uses oysters harvested from the North Atlantic coast, Chile and New Zealand.

“These oysters are a little bit more expensive,” Gold said, but safer right now.

King’s Fish House in Long Beach and Laguna Hills also has switched its oyster supplies from Puget Sound to the North Atlantic, Chile and New Zealand.

“We’ve found our sales of oysters still strong,” said Bill Matthews, director of operations for King’s Fish House. “Our strategy on oysters and other seafood is to be ready to change at a moment’s notice, so that when these warnings occur, we are prepared.”

Teru Sushi in Studio City has taken a different tack: It has stopped using oysters altogether. “We use oysters harvested from the Pacific Northwest because they are of Japanese origin,” said Yuji Horii, general manager of Teru Sushi. “A lot of customers say they still want oysters, but in Japan, no one serves oysters in the summertime. You would be kicked out of restaurants there if you asked for oysters in the summer.”

The impact of the warning on Teru Sushi’s bottom line is expected to be minor.

Marinelli said that in the long term, the increased attention to food safety will help the seafood industry because it will increase the public’s confidence that consuming seafood will not make them sick.

“Consumers are starting to ask where these shellfish come from and that is good for public safety,” he said.