Situation Update: Summary of Weekly FluView
Key Flu Indicators
According to the latest FluView report, seasonal influenza activity is low across most of the country but a wave of influenza B activity is affecting parts of the country. This week influenza B viruses account for 55% of viruses nationally and are causing an increase in influenza-like-illness in parts of the northeast especially. Below is a summary of the key indicators for the week ending April 12, 2014 (week 15):
- For the week ending April 12, 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 fifth week. ILI was above or at baseline for 15 weeks this season. However, two of 10 regions (Regions 1 and 2) reported ILI activity above their region-specific baseline levels. Additional information regarding regional activity is available through FluView Interactive.
- No states experienced high ILI activity. Three states (New Jersey, New York, Texas) and New York City experienced moderate ILI activity. Four states (Connecticut, Delaware, Massachusetts, and Rhode Island) experienced low ILI activity. Forty-three states experienced minimal ILI activity. The District of Columbia 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.
- Six states reported widespread geographic influenza activity (Connecticut, Delaware, Maine, New Jersey, New York, and Rhode Island). This is a slight increase from the five states that reported widespread activity in the previous week. Guam and four states reported regional activity. Puerto Rico, the District of Columbia and 14 states reported local activity. 24 states reported sporadic influenza activity. The U.S. Virgin Islands and two states (Kansas and Mississippi) reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
- 8,995 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2013. This translates to a cumulative overall rate of 33.2 hospitalizations per 100,000 people in the United States. The cumulative hospitalization rate for the same week last season (week 14) was 43.5 per 100,000. More data on hospitalization rates are available through FluView Interactive.
- The highest hospitalization rates are among people 65 and older (78.7 per 100,000), followed by people 50-64 years (51.5 per 100,000) and children younger than 5 years (44.5 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.
- Of the 8,995 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 decreased to 6.4% and remains below the epidemic threshold.
- One influenza-associated pediatric death was reported to CDC during the week of April 6-April 12 (week 15). The death was associated with an influenza B virus and occurred during week 14 (week ending April 5, 2014). A total of 86 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 12, 2014 increased to 14.5%. Averaged over the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 3.4% to 26.9%.
- Influenza A (H3N2), 2009 H1N1, and influenza B viruses have all been identified in the U.S. this season. 2009 H1N1 viruses have predominated overall during the 2013-14 season, though this week influenza B viruses account for the largest proportion of circulating viruses and the proportion of influenza A (H3) viruses is increasing as well. During the week ending April 12, 301 (45%) of the 675 influenza-positive tests reported to CDC were influenza A viruses and 374 (55%) were influenza B viruses. Of the 158 influenza A viruses that were subtyped, 87% were H3 viruses and 13% were 2009 H1N1 viruses. It is not uncommon for there to be a second wave of flu activity toward the end of the flu season with another seasonal influenza virus. It's possible that significant flu activity could continue into May.
- CDC has antigenically characterized 2,309 influenza viruses; 1,755 2009 H1N1 viruses, 307 influenza A (H3N2) viruses, and 247 influenza B viruses, collected since October 1, 2013.
- 1,752 (99.8%) of the 1,755 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.
- 301 (98.0%) of the 307 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.
- 172 (69.6%) of the 247 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 75 (30.4%) 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 4,899 2009 H1N1, 416 influenza A (H3N2), and 296 influenza B virus samples for resistance to the neuraminidase inhibitor influenza antiviral drugs. So far this season 56 (1.1%) 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.