Two of the cases of E. coli O157 were reported in the Saint John region in the past few days, while three were reported in the Fredericton area, said Dr. Eilish Cleary.
One of the patients was admitted to hospital, the other four were treated in hospital and released, she said.
"We believe that a couple of those cases, at least, are a very similar type of E. coli so we know that at least some of them are connected," Cleary told CBC News.
"We're still looking into the more recent cases to determine whether they're all connected or not."
Officials are also investigating whether the outbreak might be linked to a number of cases in Nova Scotia in recent weeks, said Cleary.
“A number of sources are being investigated and we are still gathering information."
E. coli O157:H7 is the same strain that killed seven people in Walkerton, Ont. in 2000.
It also led to the biggest beef recall in Canadian history this fall. The Canadian Food Inspection Agency recalled more than 1,500 beef products that were packed at XL Foods, a meat processing plant in Brooks, Alta.
E. coli O157:H7 also put two Fredericton teenagers in hospital in July, while an outbreak in Miramichi in April hospitalized at least 13 people.
This particular strain of E. coli secretes a powerful toxin that can destroy red blood cells leading to severe illness, high blood pressure and kidney damage.
Symptoms of E. coli O157 resemble gastro-intestinal illness, such as severe cramps, diarrhea, which may be bloody, abdominal pain and vomiting. Some people may develop anemia and kidney problems.
People experiencing such symptoms should seek medical advice, said Cleary.
They should also follow good hygiene practices to prevent further spread of the infection, she said.
Precautions include thorough hand washing after using the bathroom or changing diapers, peeling all raw vegetables and fruits before eating, thoroughly cooking all meat and preventing contact between cooked foods and raw poultry or other meats.
Cleary also advises people drink and eat only pasteurized dairy products.
Those most at risk of developing serious complications from E. coli include pregnant women, young children, seniors and people with a weakened immune system, such as those on chemotherapy.
During the Walkerton outbreak, at least seven people died and about 2,500 fell ill after the bacteria got into the town's water supply. The source of the contamination in that case was manure spread on a farmer's field near one of the town's wells.
The cause of the Fredericton outbreak during the summer was undetermined.
Romaine lettuce was deemed the likely source of the Miramichi outbreak last spring.