The Best source of Data on the Influenza Virus-
We have gotten such a wonderful and enthusiastic response to recent posts about infectious diseases, that I thought it would be of interest to share a great source of information- the CDC.
In particular, I want to share how the information about the influenza virus is presented every week by the CDC.
Keep in mind that viruses, like animals, are classified into a variety of species, each of which are different in many important ways. The influenza virus is one species of virus, that comes in many subtypes. Colds and flus are caused by many different species of viruses, including RSV, rhinovirus, adenovirus, coronaviruses, etc. Influenza virus causes only about 1/3 of winter-time respiratory colds and flus.
The CDC actually tracks the presence of the influenza virus in America, in great detail, for all sorts of reasons. The primary one is actually to specify which varieties are in circulation so that the right types enter each year's vaccine, and to monitor this major cause of illness.
This webpage: http://www.cdc.gov/flu/weekly/ gives anyone access to a veritable gold mine of data on the influenza virus.
Here is a brief tour of the six types of trends this web page follows on this virus:
First of all, all the data are reported weekly and usually lag 1-2 weeks behind. Today for example the page reports on Week 50 of 2014, and we are in week 52.
This is a very interesting report, as it tells us what percentage of respiratory swabs in people with colds and flus are positive for influenza. It also tracks which subtypes are in the swabs- Type A, Type B, and subtypes like the now famous H3N3. Note that as of December 13, 2014, about 25% of people with colds and flus had influenza. This means that even in the thick of the influenza onslaught, 75% of us with a cold or flu do not have an influenza infection.
The graph in this section is a bar graph with green, red, and yellow bars, color coded for the subtype of influenza virus on the swabs. Bar graphs going up means more swabs are positive for the influenza virus.
Pneumonia and influenza mortality
This is a jagged red line going up and down between two wavy black lines.
The red line is the percentage, every week, of deaths in 122 American cities due to pneumonia and influenza.
Even without an influenza virus epidemic happening, about 6-7% of all American deaths are due to pneumonia, usually in the elderly. That number goes up in the winter and down in the summer. When the red line goes above the top wavy black line, that means pneumonia and influenza deaths have reached epidemic proportions, they have not yet done this in the US as of December 13.
Influenza Pediatric Deaths
These are the green bar graphs, and they track a very sad set of facts, how many children die of influenza in the US each week. The numbers here, thankfully, are very small. About 20,000 people die of influenza infection in the US every year, but only 100 or so each year are children, so far this year that number is 11. A terrible loss, but quite rare.
Influenza associated hospitalizations
This line graph has many colored lines, one each for an age range, that tells us how many people, per 100,000, are hospitalized for influenza virus infections each week. Note that by far the most hospitalizations occur in the elderly, and as expected these rates go up in the winter.
Outpatient Illness Surveillance- This is the section I refer to most to report the progress of each winter's spread of all viral respiratory illnesses.
This is a set of different colored lines set against a dashed black line. Each line traces the percentage of visits to a doctor in the US for a fever of at least 100.0 with cough and/or sore throat.
Note how the typical year really takes off in December, peaks around New Years, and slowly fades across January and February. 2014-2015 is the red noted by the red triangles, and seems to be following a course very similar to 2012-2013.
Geographic spread of influenza virus, state-by-state
The final two graphics are state maps of the US that report levels of all viral colds and flus (green and red) and levels of influenza virus activity (Yellow and brown) for the week being reported.
1. Respiratory colds and flus do indeed peak in the winter.
2. This year is not exceptional in the rate of illness, as of December 13.
3. We are in the midst of the great peak of respiratory colds and flus for this winter.
4. Even in this peak season, about 75% of the respiratory colds and flus are from viruses other than influenza virus.
5. The detail does indicate a large proportion of the influenza virus actually circulating, unfortunately, is a subtype not included in this year's influenza vaccine. Keep in mind this vaccine is manufactured every spring and as such, has to be a prediction of what subtypes will circulate the following winter. This year the mismatch was significant. FluMist offers more protection across varying subtypes than the injected flu shot.
6. MOST importantly. As with most years reported, infection with influenza in healthy children, although a miserable experience, tends to be quite harmless. At it's worst, so far this year, about 99.99% of children who get this infection recover without need of hospitalization.
Again, we offer this guide to the CDC data, since we find it helpful and reassuring. We will continue to report the trends for colds and flus, and the influenza virus, as the season progresses.
Here is to a Happy and Healthy New Year,
Dr. Arthur Lavin
*Disclaimer* The comments contained in this electronic source of information do not constitute and are not designed to imply that they constitute any form of individual medical advice. The information provided is purely for informational purposes only and not relevant to any person's particular medical condition or situation. If you have any medical concerns about yourself or your family please contact your physician immediately. In order to provide our patients the best uninfluenced information that science has to offer,we do not accept samples of drugs, advertising tchotchkes, money, food, or any item from outside vendors.