Nearly half of US states are reporting widespread flu activity, driven by the 2009 H1N1 virus, which is taking a toll on younger children and working-age adults, according to the latest surveillance and media reports.
The US Centers for Disease Control and Prevention (CDC) said all 10 of its regions are reporting activity above their specific baselines as measured by the percentage of clinic visits for flu-like illness.
Also, it said 25 states are reporting geographically widespread activity, up from 10 the previous week. The system the CDC uses to gauge doctor visits for flu in different parts of the country shows that 20 states are reporting high activity, up from 6 the week before.
The percentage of respiratory samples that tested positive for flu also rose again, weighing in at 26.7%, up from 24.1% the previous week, the CDC said. About 97% of the viruses were influenza A, and of those subtyped, nearly all (99.2%) were the 2009 H1N1 virus.
Another marker that rose again last week was the seasonal cumulative rate of hospitalization for flu, up from 4.3 per 100,000 to 5.8 per 100,000 population. The 2009 H1N1 virus was responsible for 98.2% of the influenza A infections registered in the CDC flu hospitalization tracking system.
The most common underlying conditions in adults hospitalized for flu were obesity, metabolic disorders, and cardiovascular disease. For kids they were asthma, obesity, and neurologic conditions. However, 43.5% of hospitalized youngsters had no known chronic medical condition that would make them more vulnerable to flu complications.
One marker that stayed below its seasonal baseline was overall deaths from pneumonia and flu. The CDC received two more reports of pediatric flu deaths, raising the season's total to six. Of the newest deaths, one was related to the 2009 H1N1 virus and the other was from an unsubtyped influenza A virus.
Media reports reflect national patterns
Brisk flu activity in the United States is also reflected in news headlines. For example, the University of Michigan Health System (UMHS) said today in a statement that more than a dozen adults and children are on life support at its hospitals, with most of them young and otherwise healthy. Many were transferred from other hospitals because of their severe infections, and most are infected with the 2009 H1N1 strain, the statement said.
The rapid uptick in flu prompted the UMHS to issue temporary visitor restrictions, and it urged the state's unvaccinated residents to get their flu shots as soon as possible. UMHS said that although the vaccine doesn't guarantee a person won't get the flu, it greatly reduces the chances.
Lena Napolitano, MD, associate chair for critical care in the University of Michigan department of surgery, said in the statement, "We are seeing the same thing we saw in 2009 and early 2010, with [intensive care units] full of people in their 30s, 40s and 50s who need advanced life support for flu-related illness, except this year, protection has been available since September." She noted that life-threatening lung and kidney problems, as well as septic shock, are among patients' flu complications.
In southern Texas, Hildago County health officials have confirmed six deaths from the 2009 H1N1 virus since Thanksgiving, the Associated Press (AP) reported today. Eduardo Olivarez, chief administrative officer with Hildago County Health and Human Services, told the AP that five of the patients who died were adults, one was a child, and all had underlying medical conditions.
Reports of spikes in 2009 H1N1 activity, which began in a handful of southern states last month, have spurred reminders from federal health officials for the public to get vaccinated and for health providers to review antiviral recommendations, especially for patients at high risk for flu complications.
The CDC has said that although the 2009 H1N1 disease patterns are similar to those seen during the pandemic years, so far there are no signs of changes in the virus, the brisk flu activity isn't surprising at this time of year, and it's not too late for people to be vaccinated.
H1N1 marks Mexican, Canadian flu seasons
Meanwhile, flu activity—dominated by 2009 H1N1—continues to climb in Mexico and Canada, which triggered an epidemiologic update yesterday from the Pan American Health Organization (PAHO). It said influenza activity in North America is at expected levels for this time of year and that the 2009 H1N1 virus is circulating like other seasonal flu viruses and merits the same clinical management and response actions.
However, PAHO urged member countries to continue surveillance efforts to detect any unusual viral behavior or any new subtypes that emerge. It also urged countries to press ahead with their seasonal flu vaccination efforts.
The Public Health Agency of Canada (PHAC) said in its latest weekly flu update today that activity has continued to increase sharply over the past 2 weeks and that about 90% of the subtyped viruses are the 2009 H1N1 strain. It noted that a greater proportion of cases have been reported in adults aged 20 to 64 years, a change from last season, when H3N2 was the predominant strain.
Two hot spots of widespread activity in Canada are both in Alberta, in the regions near Calgary and Edmonton, according to the PHAC.
In Europe, health officials still see no sign of sustained flu activity, with low-intensity activity in reporting countries, the European Centre for Disease Prevention and Control (ECDC) said today. It noted that low levels of reporting over the holiday weeks make it difficult to provide comprehensive analysis of the most recent flu activity.
Jan 3 CDC FluView report
Jan 2 PAHO epidemiological update
Jan 3 PHAC FluWatch report
Jan 3 UMHS statement
Jan 3 AP story
Jan 3 ECDC weekly influenza surveillance report