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1st Quarter 2001 Influenza Data Analysis (USA)


Installed Approximately 10 May 2001 - Latest Update - 25 Dec 2016
Additions or changes are in bold.

The following Week 16 Map was prepared based on data published in the Week 18 2001 regional reports by the World Health Organization/National Respiratory and Enteric Virus Surveillance System WHO/NREVSS.

Percent of Positive Influenza Isolates versus Region - Week 16 - 2001

The following Percent of Positive Influenza Isolates versus Region data, for weeks 10-18 2001, were extracted from WHO/NREVSS regional reports published in the CDC's Influenza Summary Update for week 18 2001. For week 16, three regions have notably higher percentages than might be expected based on the general behavior of the surrounding data.


New England (NE) West North Central (WNC) West South Central (WSC)
Mid Atlantic (MA) South Atlantic (SA) Mountain (MTN)
East North Central (ENC) East South Central (ESC) Pacific (PAC)

Week NE MA ENC WNC SA ESC WSC MTN PAC
10 1.6 9.4 9.3 6.2 9.3 5.1 7.1 7.1 10.1
11 11.4 7 7.7 6.8 6.5 1 2.7 4.9 8.8
12 6.5 4.7 6.6 5.4 10.5 3.4 0.9 2.9 10.6
13 17.9 1.9 3.8 5.2 5.6 2 0.8 2.1 0.5
14 15.4 2.5 6.6 2.8 3.3 0 0 1 0.3
15 0 2.5 4.1 2.8 4.6 0 0 0.5 0.4
16 0 5.7* 2.7 1.5 2 3.7* 0 1.7 5.8*
17 0 0 1.6 0 0 0 0 1.9 0
18 0 No Data No Data 0 0 0 0 0 0

* Week 16 values marked with asterisks may be higher than normally expected.

All influenza isolates identified for week 16 (totaling 28) were type B. These show up as a bump on the seasonal graph of influenza isolates in the CDC's weekly report for week 18. Please note that this detailed information is not archived with each weekly CDC report.

The next graph shows how the influenza like illness (ILI) reports tapered off (by region) in the final weeks of the 2000-2001 influenza season.

Total Number of Isolates Tested by Week
Total Number of Influenza Like Illnesses Tested by Week

A Look at Updated Seasonal Data

Added 9 June 2001 - Revised 10 June 2001

Data published in the CDC's week 20 report (where previously untested samples are included) decreases the overall prominence of the week 16 influenza type B bump discussed above. In essence, the week 16 bump, which I suggested might relate to The Pacific Dust Express, essentially disappears when expressed as a percent of the total number of samples tested. (See the WHO/NREVSS Influenza Isolates graph in CDC's Influenza Summary Update for week 20.)

When the data is looked at from a region to region basis, two of the week 16 bumps remain in full strength. The third bump, in the Pacific region, takes a hit.

The places where the percent positive values have changed slightly are denoted by the presence of a plus or minus sign following the percent value. A plus means that the latest percent is greater than that for week 18 and minus means less than for week 18. In four instances there were dramatic changes. These are denoted by ++ and --.

New England (NE) West North Central (WNC) West South Central (WSC)
Mid Atlantic (MA) South Atlantic (SA) Mountain (MTN)
East North Central (ENC) East South Central (ESC) Pacific (PAC)

Week NE MA ENC WNC SA ESC WSC MTN PAC
10 1.4- 9.4 9.3 6.2 9.3 5.1 7.1 7.1 10.1
11 8.2- 7 8+ 6.8 6.5 1 2.7 4.9 8.8
12 4- 4.7 6.9+ 6.4+ 10.4- 3.4 0.9 2.9 10.6
13 11.1- 1.9 4.5+ 5.5+ 5.6 2 0.8 2.1 9.5++
14 15.4 2.5 6.9+ 3.2+ 3.2- 0 0 1 8.4++
15 0 2.4- 4- 3.6+ 4.4- 0 0 0.5 3.3++
16 0 5.8+* 1.5- 1.7+ 1.6- 3.7* 0 1.4- 3.2--
17 0 0 0.9- 0 0 0 0 1.4- 0
18 0 0 0.9 0 0 0 0 0 0.5+
19 6.7 0 0 0 0 0 2.6 0 0
20 20 10 0 0 0 0 0 0 0.9+

Below is a graph of the Influenza B isolates showing both week 18 and week 20 data. The blue and green lines behind the data bars represent smoothed isolate counts.

Just below this graph is a plot showing the weekly differences between the weekly isolate counts and the smoothed counts. These are expressed as percents of the smoothed counts.


Total B Isolates Identified by Week - U.S.A. - 2001

A Venus Bump?

For week 18 an intriguing increase in the total number of Influenza Like Illnesses tested appears in four (possibly five) of the nine reporting regions. These are the (2) Mid Atlantic, (3) East North Central, (6) East South Central, (7) West South Central (maybe), and (8) Mountain regions.

The following four graphs show total numbers of Influenza Like Illness specimens tested per week by WHO/NREVSS for each of the nine reporting regions in the United States. (Each regional graph has two branches. The lower branches represent data published in the week 18 reports. The upper branches reflect the data published in the week 20 reports.)

Week 18 (ending Friday May 5, 2001) encompasses the beginning of the 30 to 60 days hypothetical Flu-Watch period, following the 29 March 2001 Venus inferior conjunction. .

Amongst the week 18 Influenza Like Illnesses which did not turn out to be recognizable as A(H1N1), A(H3N2), A(Unknown), or B viruses there may be some visitors worth getting to know.

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