An outbreak of the H1N1 virus in an Edmonton hospital has prompted health officials to close one of its units.

Alberta Health Services confirmed Tuesday that a ward at the Stollery Children鈥檚 Hospital was still operating, but was not accepting new patients because of three lab-confirmed flu cases. Health officials say this is standard procedure when there are more than two confirmed cases.

鈥淲hat happened at the Stollery is something that does happen from time to time,鈥� said Dr. Gerry Predy, senior medical officer for Alberta Health Services.

Health officials say the ward at the Stollery Children鈥檚 Hospital is following outbreak control procedure, which also means that staff are required to be diligent about wearing protective gear, and staff who are not immunized are asked to take antiviral medication. 

The health authority鈥檚 most recent statistics show 256 lab-confirmed cases of the flu in Edmonton, 236 of which are the H1N1 strain. Of those confirmed cases, 31 have required hospitalization.

Across Alberta, 621 of the 662 lab-confirmed flu cases have been identified as the H1N1 strain. But officials say the actual number of H1N1 cases may be higher as tests are only performed on the most severe cases.

Although the number of flu cases in Alberta has surged in recent weeks, health officials say it鈥檚 relatively normal for this time of year.

However, officials warn the strain can affect people under 65.

鈥淚t is a concern because younger people can be more severely afflicted than seniors in nursing homes,鈥� infectious disease specialist Dr. Neil Rau told 麻豆影视 Channel.

While doctors say fatalities are rare, Rau says younger people with underlying health problems like asthma, obesity and diabetes can be affected.

鈥淭he predominant strain is the H1N1 strain rather than the usual seasonal strain that we鈥檝e seen over the past three or four years since the pandemic year of 2009-2010.鈥�

While it鈥檚 not clear why the H1N1 strain -- which hasn鈥檛 changed over the last five years -- made a comeback this year, Rau speculates people鈥檚 immunity to the virus has decreased over time. 

鈥淲e鈥檝e also got the issue of kids under five who never actually saw the pandemic stream,鈥� he said.

Meanwhile, Alberta Health Services will open four mass flu immunization clinics across the province this week in an effort to contain the outbreak.