# 5054
Influenza continues to circulate at low levels across the United States, with fewer than 7% of ILI (Influenza-like illness) samples submitted for analysis testing positive for the flu.
First some highlights from this week’s FluView report, and then some discussion about the other 93% of flu-like illnesses that weren’t influenza.
2010-2011 Influenza Season Week 44 ending November 6, 2010
All data are preliminary and may change as more reports are received.
Synopsis:
During week 44 (October 31-November 6, 2010), influenza activity remained low in the United States.
- Of 2,704 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division, 185 (6.8%) were positive for influenza.
- Two human infections with novel influenza A viruses were reported.
- The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
- One influenza-associated pediatric death was reported and was associated with an influenza A virus for which the subtype was undetermined.
- The proportion of outpatient visits for influenza-like illness (ILI), 1.3%, was below the national baseline, 2.5%. All 10 regions reported ILI below region-specific baseline levels; one state experienced low ILI activity, 49 states experienced minimal ILI activity.
- Geographic spread of influenza in three states was reported as local; the District of Columbia, Puerto Rico, and 34 states reported sporadic activity; Guam and 13 states reported no influenza activity, and the U.S. Virgin Islands did not report.
As you can see, last year’s novel H1N1 virus was identified in only a small fraction (8%) of the positive influenza tests returned last week, while Influenza B and H3N2 appeared far more frequently.
P&I (Pneumonia & Influenza) related deaths were once again below the epidemic threshold, although they did climb a bit in the latest reporting week.
The `big’ story of the week was, of course, the release of information regarding two novel influenza A(H3N2) swine-origin flu virus infections.
Novel Influenza A Virus:
Two cases of human infection with a novel influenza A virus were reported: one case by the Wisconsin Department of Health Services and one case by the Pennsylvania Department of Health. Both patients were infected with a swine origin influenza A (H3N2) virus similar to the three other swine origin influenza A (H3N2) viruses previously identified in 2009 and 2010. The Wisconsin case reported contact with pigs in the week preceding symptom onset on September 8, 2010 and required hospitalization. No contact with pigs has been identified in the Pennsylvania case in the week before symptom onset on October 24, 2010; however the case lives in an area close to pig farms. Both patients have fully recovered from their illness. The cases are not related and the viruses from these two cases have some genetic differences, indicating that they did not come from the same source.
Although both investigations are ongoing, there is no evidence of human-to-human transmission with this virus in either case. Early identification and investigation of human infections with novel influenza A viruses is critical to evaluate the extent of the outbreak and possible human-to-human transmission. Surveillance for human infections with novel influenza A viruses continues year round.
For additional information on these cases and swine influenza, see
For most people, respiratory infections are pretty much divided up into three broad categories; colds, the flu, and most seriously, pneumonia.
But in reality, the spectrum of common respiratory viruses is far more diverse and includes such pathogens as metapneumovirus, parainfluenzavirus, respiratory syncytial virus (RSV), any of the myriad Rhinoviruses (Common cold), and a number of varieties of adenovirus.
Last year, during the height of the fall wave of the H1N1 pandemic, I posted the following graphic on my blog.
Of the more than 10,000 samples submitted for testing during the 1st week of October 2009, more than 72% – almost 3/4ths – came back negative for influenza.
Although testing may miss some cases (samples degrade, viral shedding at the time of sampling may have been low, etc), it is pretty obvious that a lot of flu-like illnesses are caused by something other than influenza.
And frankly, except for a few peak weeks every flu season, the percentage of samples testing positive for influenza A is usually less than 10%.
Which is why doctors generally refer to ILIs, or Influenza-like Illnesses (or sometimes ARI Acute Respiratory Infection), when making a clinical diagnosis.
Testing to find out exactly what kind of virus a patient may have is time consuming, expensive, and not usually justified. By the time test results come back, most patients will have recovered.
One of the reasons that many people dismiss influenza as a serious threat is because often, when they’ve thought they had the flu, they had something else entirely.
And this can also lead people who got the flu vaccine, and later got `the flu’, to erroneously conclude the vaccine didn’t protect them.
Of course, even non-influenza viral infections can cause significant morbidity and mortality – particularly among the very young, the very old, and those with comorbid conditions.
While it is estimated that, in a normal year, between 7% and 10% of Americans catch the `flu’, far more of us will endure some other kind of respiratory misery during cold and flu season.
So staying home when you have a flu-like illness, washing or sanitizing your hands often during the day, and covering your coughs and sneezes are all important steps you can take to protect yourself, and others, from respiratory infections this winter.
No matter what the cause.
