Mayor Tom Menino urges residents to get vaccinated as city confronts 700 confirmed cases amid fears of nationwide danger

The city of Boston has declared a public health emergency as fears of a nationwide flu outbreak intensify.

Mayor Thomas Menino urged residents to get vaccinated against flu, as the city scrambled to deal with 700 confirmed cases so far – compared to just 70 cases during the whole of last year's flu season.

The move came as experts warned the current flu strain is one of the worst in the past 10 years. Data Google's Flu Trends indicator, which has proved a reliable indicator of outbreaks, shows higher flu activity than at any point in the previous six years.

"This is the worst flu season we've seen since 2009, and people should take the threat of flu seriously," Menino said in a statement on Wednesday.

"This is not only a health concern," he said, "but also an economic concern for families, and I'm urging residents to get vaccinated if they haven't already. It's the best thing you can do to protect yourself and your family. If you're sick, please stay home from work or school."

The city's declaration of a health emergency was "very unusual", Dr Anita Barry, director of Boston's Infectious Disease Bureau told the Associated Press.

Barry said it was designed to raise awareness about the severity of the flu season and to make available public resources, such as providing health centers with vaccine.

The main strain of flu this year is H3N2, which is known to cause relatively severe illness.

Boston has had four flu-related deaths this season, while Massachusetts has had 18, according to the state's department of public health. It said the percentage of doctor visits statewide that are for flu-like illness – described as fever, body aches, coughing, runny nose, and fatigue – is now above 4%. Last year only 1% of visits were due to the flu at the season's peak.

Earlier this week Tim Skinner of the federal Centers for Disease Control and Prevention warned that this winter's flu outbreak is likely to be among the worst in the past decade. The season is looking likely to be "moderate to severe", Skinner told the New York Daily News. "In the past 10 years we have seen just two or three like it."

Google's flu trends tool suggests that this year could be one of the worst since the company began tracking outbreaks in 2006. The internet giant tracks search terms relating to flu, mapping out the results on its non-profit website.

The tracking tool, which was endorsed by a 21-month scientific study last year, has mapped official CDC data on flu outbreaks remarkably closely since it was first published. The flu activity for December 2012 is higher than any other year recorded by Google, and higher than the more traditionally flu-heavy month of February.

Flu activity is regarded as "intense" across most of the contiguous states, with cases slightly less severe along the west coast. The CDC is due to release its latest flu count figures on Friday.

© Guardian News and Media 2013