The CDC data above shows that the occurrence of flu generally peaks in February; the data below from Google insights : flu symptoms, not surprisingly, has a similar peak in February.

Google insights, which uses the same data as Google Flu Trends, shows quite a different pattern for flu shot (below), which peaks in October or November (Flu vaccine peaks similarly).

How about searching for just the word flu (below)? — Interestingly, this seems to combine the peaks in the two graphics above, for flu symptoms and flu shot. The exaggerated peaks in 2004 and 2005 likely are caused by peoples’ concerns about vaccine shortage (more on this in accompanying posting, Google Flu Trends: Kudos & Complications).

Looking at the evidence of these graphics from Google Insights, it seems likely that the Google Flu Trends team is excluding search terms relating to flu vaccine, and concentrating on terms that relate to symptoms. See confirmation of this in accompanying posting, Google Flu Trends: The Iowa Connection.

The data shown here seems to indicate that for a seasonal disease in which there is a vaccine, the search patterns for “disease: symptoms,” “disease: vaccine/shot,” and the disease term itself differ, correlated with the time in the year when the disease occurs and when the vaccine is given. This idea is confirmed by Google Insights data for pneumonia, another respiratory disease that has a vaccine. The patterns are similar to flu, with high peaks for pneumonia shot in October, and somewhat lower peaks for pneumonia and pneumonia symptoms in February.

Bronchitis — A disease with no vaccine

Bronchitis is a respiratory disease condition that does not have a vaccine. As the graphics from Google Insights below show, the pattern is different from flu and pneumonia — The peaks for the disease itself (bronchitis, below) and for the disease with symptoms is much the same, making it less complicated to track search patterns — Apparently the people who search for the disease are in fact people who have the disease.

Bronchitis symptoms, from Google Insights.

** This is one of a group of three articles on Google Flu Trends:

Together, these articles suggest that, although it’s difficult to know with assurance because Google has not revealed the search terms that they use for GFT, it seems likely that they’ve done a good job in working around the complications of flu-related search patterns.

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