Situation Update: Summary of Weekly FluView
Key Flu Indicators
According to the latest FluView report, seasonal influenza activity is declining across the nation, though flu viruses continue to circulate and cause illness in parts of the U.S. Below is a summary of the key indicators for the week ending April 5, 2014 (week 14):
- For the week ending April 5, the national proportion of people seeing their health care provider for influenza-like illness (ILI) decreased and remains below the national baseline of 2.0% for the fourth week. ILI was above or at baseline for 15 weeks this season. Two of 10 regions reported ILI activity at or above their region-specific baseline levels. Additional information regarding regional activity is available through FluView Interactive.
- New York City experienced high ILI activity; the same as in the previous week. One state (New York) experienced moderate ILI activity. Five states (Connecticut, Delaware, Minnesota, New Jersey, and Texas) experienced low ILI activity. Forty-three states experienced minimal ILI activity. The District of Columbia and one state (Utah) did not have sufficient data to calculate an activity level. ILI activity data indicate the amount of flu-like illness that is occurring in each state.
- Five states reported widespread geographic influenza activity. This is the same number of states that reported widespread activity in the previous week. Guam and four states reported regional activity. The District of Columbia and 15 states reported local activity. Puerto Rico and 25 states reported sporadic influenza activity. The U.S. Virgin Islands and one state (Mississippi) reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
- 8,777 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2013. This translates to a cumulative overall rate of 32.4 hospitalizations per 100,000 people in the United States. The cumulative hospitalization rate for the same week last season (week 14) was 43.1 per 100,000. More data on hospitalization rates are available through FluView Interactive.
- The highest hospitalization rates are among people 65 and older (75.4 per 100,000), followed by people 50-64 years (50.5 per 100,000) and children younger than 5 years (43.7 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.
- Of the 8,777 influenza-associated hospitalizations that have been reported this season, approximately 60% have been in people 18 to 64 years old. This trend of increased hospitalizations among younger people was also seen during the 2009 H1N1 pandemic.
- Hospitalization data are collected from 13 states and represent approximately 8.5% of the total U.S. population. The number of hospitalizations reported does not reflect the actual total number of influenza-associated hospitalizations in the United States.
- The proportion of deaths attributed to pneumonia and influenza (P&I) based on the 122 Cities Mortality Reporting System increased slightly to 6.8% and remains below the epidemic threshold.
- Three influenza-associated pediatric deaths were reported to CDC during the week of March 30-April 5 (week 14). One death was associated with an influenza A virus for which no subtyping was performed, and two deaths were associated with an influenza B virus. A total of 85 influenza-associated pediatric deaths have been reported for the 2013-2014 season at this time. Additional information about the pediatric deaths from this season and previous seasons is available through FluView Interactive.
- Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week ending April 5, 2014 increased slightly to 13.4%. Averaged over the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 3.5% to 26.4%.
- Influenza A (H3N2), 2009 H1N1, and influenza B viruses have all been identified in the U.S. this season. The 2009 H1N1 viruses have predominated during the 2013-14 season, though the proportion of influenza B viruses is now increasing. During the week ending April 5, 302 (44%) of the 685 influenza-positive tests reported to CDC were influenza A viruses and 383 (56%) were influenza B viruses. Of the 181 influenza A viruses that were subtyped, 69% were H3 viruses and 31% were 2009 H1N1 viruses.
- CDC has antigenically characterized 2,207 influenza viruses; 1,753 2009 H1N1 viruses, 270 influenza A (H3N2) viruses, and 184 influenza B viruses, collected since October 1, 2013.
- 1,752 (99.9%) of the 1,753 2009 H1N1 viruses tested were characterized as A/California/7/2009-like. This is the influenza A (H1N1) component of the Northern Hemisphere quadrivalent and trivalent vaccines for the 2013-2014 season.
- 264 (97.8%) of the 270 influenza A (H3N2) viruses tested were characterized as Texas/50/2012-like. This is the influenza A (H3N2) component of the Northern Hemisphere quadrivalent and trivalent vaccines for the 2013-2014 season.
- 124 (67%) of the 184 influenza B viruses tested belonged to the B/Yamagata lineage of viruses, and were characterized as B/Massachusetts/02/2012-like. This is an influenza B component for the 2013-2014 Northern Hemisphere quadrivalent and trivalent influenza vaccines.
- The 60 (33%) other influenza B viruses belonged to the B/Victoria lineage of viruses, and were characterized as B/Brisbane/60/2008-like. This is the recommended influenza B component of the 2013-2014 Northern Hemisphere quadrivalent influenza vaccine.
- Since October 1, 2013, CDC has tested 4,817 2009 H1N1, 381 influenza A (H3N2), and 247 influenza B virus samples for resistance to the neuraminidase inhibitor influenza antiviral drugs. While the vast majority of the 2009 H1N1 viruses that have been tested are sensitive to oseltamivir and zanamivir, one additional 2009 H1N1 virus showed resistance to oseltamivir and were reported during the week ending April 5. So far this season 56 (1.2%) 2009 H1N1 viruses have shown resistance to oseltamivir. No influenza A (H3N2) or influenza B viruses have shown resistance to oseltamivir. No viruses have shown resistance to zanamivir.
- The neuraminidase inhibitors oseltamivir and zanamivir are currently the only recommended influenza antiviral drugs.
- As in recent past seasons, high levels of resistance to the adamantanes (amantadine and rimantadine) continue to persist among 2009 H1N1 and influenza A (H3N2) viruses. Adamantanes are not effective against influenza B viruses. Adamantanes are not recommended for use against influenza this season.
Note: Delays in reporting may mean that data changes over time. The most up to date data for all weeks during the 2013-2014 season can be found on the current FluView.