Saturday, February 22, 2014

CDC reports high FLU death rates in young Americans, but may be overestimating by 300%

CDC notes the following, where P stands for pneumonia and I stands for influenza:
Among 14,628 P&I deaths reported through the 122 Cities Mortality Reporting System from September 29, 2013 to February 8, 2014, a total of 571 (3.9%) were influenza-associated (i.e., they had influenza listed on the death certificate as an underlying or contributing cause of death), of which 352 (62%) were in persons aged 25-64 years, 194 (34%) in persons aged ≥65 years, and 25 (4%) in persons aged 0-24 years.
The first thing to notice is that CDC likes to lump pneumonia and influenza numbers together.  But when you only look at deaths, only 3.9% of deaths associated with pneumonia and/or influenza (in an area of 27 million Americans used by CDC for medical surveillance purposes) actually had influenza listed as a cause or contributor to death.  That means over 96% were due to pneumonia in the absence of flu.

Let's look at these numbers more carefully. From end September of last year until 2 weeks ago today, CDC says 571 people died (in 122 cities) who had influenza listed on their death certificate. Twenty-five were allegedly aged 0 through 24 years old.  Remember, this is in a group of only 27 million Americans.  If you extrapolated this death rate to 317.5 million Americans, you would have 294 deaths in the 0-24 years age group this year.

Except it seems we have no where near that number.  CDC never measures total deaths from influenza by death certificate. Nor does it measure total US deaths associated with influenza from other records. But flu deaths in children are required to be reported, so CDC does keep records of flu-associated deaths in children aged 0-18 years

In the next paragraph, CDC says that only 50 deaths in children associated with influenza have occurred in the entire US this flu season, through Feb. 8. Checking the Fluview website, we see 2 more pediatric deaths were reported between Feb 9 and Feb. 15.

Now look at hospitalizations for different age groups for lab-confirmed influenza (Figure 3).  To estimate actual flu death rates in those aged 18-24, for whom CDC does not provide specific numbers, I will use 2014 flu hospitalization rates by age as a rough estimate of flu-associated death rates, by age. I am doing this because there are no good overall US statistics for flu-associated deaths in those over 18.

The following graph shows that children aged 0-4 years have the third highest rate of severe illness (requiring hospitalization), after those 50-64 and over 65 years.  Hospitalizations in those aged 5-17 occur at only 15% of the rate of younger children, and people aged 18-49 are hospitalized at half the rate of those aged 0-4.

Using comparative hospitalization rates to extrapolate flu deaths for Americans aged 0-24 from the data on those aged 0-18, you would only expect about 25 additional deaths in those aged 18-24, or a total of 75 deaths in those aged 0-24 throughout the US through Feb. 8, 2014--instead of 294 (the extrapolation using CDC's 121 Cities data).

Therefore, either the 121 cites data dramatically overestimated flu deaths this season in those under 25, or the pediatric death reports are extremely low.  But they are in line with those of previous, recent years.

One explanation might be that most of the deaths for which death certificates list flu as a contributor, were not considered flu deaths and were therefore not reported as such to CDC.  The discrepancy cannot be explained at this point, but it does suggest that CDC's announcements of high mortality in children and young adults could be off -- perhaps by 300%.

FIGURE 3. Rates of hospitalization for laboratory-confirmed influenza, by age group and surveillance week - FluSurv-NET,* 2013-14
The figure above shows rates of hospitalization for laboratory-confirmed influenza, by age group and surveillance week during 2013–14. CDC monitors hospitalizations associated with laboratory-confirmed influenza in adults and children through the Influenza Hospitalization Surveillance Network (FluSurv-Net), which covers approximately 27 million persons, 8.5% of the U.S. population. From October 1, 2013 through February 8, 2014 (week 6), a total of 6,655 laboratory-confirmed influenza-associated hospitalizations were reported. This yields a rate of 24.6 hospitalizations per 100,000 population.

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