Have We Peaked (in the US), Or Is Class Still In Session?

[Missouriwatcher]

By comparison, A/2009 H1N1 has been most prominent in Region 4 since week 2 and in Region 5 since week 4.
http://www.cdc.gov/flu/weekly/regions2010-2011/data/whoreg4t.htm
http://www.cdc.gov/flu/weekly/regions2010-2011/data/whoreg5t.htm
These two regions have had the most pediatric deaths. Looking at cause of all pediatric deaths, A/2009 H1N1 has been implicated in 12 of the 55 pediatric deaths and an additional 11 deaths have A as the cause with no subtype.

A/2009 H1N1 became the most prominent in week 7 for Regions 2, 3 and 9 (possibly in week 8 for Regions 1 and 8).
http://www.cdc.gov/flu/weekly/regions2010-2011/data/whoreg2t.htm
http://www.cdc.gov/flu/weekly/regions2010-2011/data/whoreg3t.htm
http://www.cdc.gov/flu/weekly/regions2010-2011/data/whoreg9t.htm
It is a far cry to say this has peaked, since states like AZ are delaying reports due to ?volume of cases?. Looking at some of the isolate graphs reported by WHO/NREVSS Collaborating Laboratories, it appears that the ?percent positive? is continuing upward in some regions and remaining quite high in others.

Additionally, hospitalizations and deaths are behind by weeks. For example, comparing week 48 in week 8, a new hospitalization was reported that was not there in week 7. http://www.cdc.gov/flu/weekly/weeklyarchives2010-2011/data/AHDRA07.htm
http://www.cdc.gov/flu/weekly/weeklyarchives2010-2011/data/AHDRA08.htm
For weeks 2 & 3, deaths and hospitalizations were fairly resolved by week 6 report of weeks 2 & 3 when compared to week 5.
http://www.cdc.gov/flu/weekly/weeklyarchives2010-2011/data/AHDRA05.htm
http://www.cdc.gov/flu/weekly/weeklyarchives2010-2011/data/AHDRA06.htm
Now looking at week 8 hospitalizations and deaths, 17 out of the 24 jurisdictions that have been reporting, have reported. The deaths are high, for the number of hospitalizations at this point. It could be several weeks before the rest of the jurisdictions report for week 8. Last season (at peak) there were 37 jurisdictions reporting 5,007 hospitalizations and 191 deaths. So far, week 7 reported 1,515 hospitalizations and 23 deaths (19 jurisdictions). Quite low by comparison, yet just beginning?
http://www.cdc.gov/flu/weekly/weeklyarchives2010-2011/data/AHDRA08.htm
http://www.cdc.gov/flu/weekly/weeklyarchives2009-2010/data/AHDRA20.htm

Interestingly, the ILI is showing a downward trend. Is this due to a backlog? ISDS Distribute, supposedly with the most up-to-date stats, has ED ILI drastically decreasing. http://isdsdistribute.org/

Are we at the beginning or the end? Perhaps the ?herd immunity? and vaccination campaign are paying off and we are in the homestretch. Time will tell.

 

[JimO]

Re: Are We at the Beginning or the End?

Re: Are We at the Beginning or the End?

The following is my amateur opinion because although I am a scientist (hydrogeologist), I have no credentials in medicine, diseases, epidemiology, or genetics. I do, however, have a lot of experience in data analysis, evaluating trends in data, etc. But, this is just an opinion based on what I have many spent hours studying over the past two years.

I sincerely hope that I am wrong, but I think we are at the beginning of whatever pH1N1 has in store for us. The decrease in %ILI could be explained by the significant drop in RSV cases over the past three weeks. Even decreases in percent positive influenza could be the result of fewer samples being taken in many jurisdictions, but I have noticed that H3N2 has decreased sharply in many places when pH1N1 shows up; however, the rate that H3N2 drops is typically higher than the rate that pH1N1 increases, so the net result is a decrease in Flu A cases.

One other potential complicating factor is that in states where pH1N1 has been detected since December, they might be seeing predominantly viruses that do not carry some of the mutations exhibited in samples collected later in the UK epidemic (this is my speculation and not based on genetic information). So, in those areas pH1N1 might not have been a factor through the end of 2010. But, if a mutated strain is circulating, a glimpse of what that could do appears to be unfolding in the Pittsburgh area. The sequences from samples collected from severe and fatal cases in PA are similar to those collected in the UK in late December and early January. Also, the DoD recently released 17 sequences having the same mutations. These samples were collected from people with severe cases of pH1N1 and who all had been vaccinated.

So, again, I sincerely hope to be wrong, but I expect to see the %ILI to drop for another two weeks or so nationally, but then I expect to see pH1N1 start becoming the dominant A strain (it seems to coexist well with Flu B). In some places we will see a sharp rise in hospitalizations, sudden deaths of young healthy people, etc. because the mutated strain will be dominant. In places where the strain that resembles that for which the vaccine is protective, it will be interesting to see if the mutated strain will displace it.

I think we need to keep an eye on PA, AZ, southern CA, and some of the New England states (CT, RI, and NH), where pH1N1 is rising more rapidly. I think we will continue to see overall declines in flu cases in the southeast where Flu B and H3N2 have made it a rough flu season so far, particularly in LA, AL, and GA, but where pH1N1 has been all but absent. But, I believe they will have a second peak of pH1N1.

I'm concerned that TN is going through that now, but their surveillance data is somewhat limited. However, there have been reports of severe cases and higher numbers of hospitalizations in Vanderbilt hospitals recently. Sudden deaths of relatively young, healthy people have been reported in recent weeks: a 25-yo pregnant woman (http://www.flutrackers.com/forum/showthread.php?t=162481), a 50F teacher (http://www.flutrackers.com/forum/showthread.php?t=162960), a 19F (http://www.flutrackers.com/forum/showthread.php?t=162411), and a 62M teacher (http://www.flutrackers.com/forum/showthread.php?t=161341), who died of multiple organ failure.

I pray it fizzles out, but I fear it will get a lot worse before it gets better.

Interestingly, the ILI is showing a downward trend. Is this due to a backlog? ISDS Distribute, supposedly with the most up-to-date stats, has ED ILI drastically decreasing. http://isdsdistribute.org/

Are we at the beginning or the end? Perhaps the ?herd immunity? and vaccination campaign are paying off and we are in the homestretch. Time will tell.

 

[Laidback Al]

Re: Are We at the Beginning or the End of Influenza Season in the US?

Re: Are We at the Beginning or the End of Influenza Season in the US?

The definition of the ?flu season? in the U.S. varies. Sometimes it is defined on an absolute calendar year from September 1 of one year to August 31 of the following year. Other times the flu season is defined as covering only part of the year on a relative calendar basis. In these situations, the start of flu season is defined as beginning in week 40 of the preceding year with the season ending on week 20 of the following year (Sunday to Saturday week). The increase in influenza cases of p(H1N1) after week 20 in 2009 pandemic is a reminder that it is premature to speculate about the course of influenza infections over the coming weeks and months. We will have to wait and see what happens.

While one can always make predictions about the future, It is impossible to discern the direction of a trend in the here and now. Trends are only observable retrospectively, i.e. by looking at past data after the events have occurred.

 

[Missouriwatcher]

Have We Peaked (in the US), Or Is Class Still In Session?

While one can always make predictions about the future, It is impossible to discern the direction of a trend in the here and now. Trends are only observable retrospectively, i.e. by looking at past data after the events have occurred.

Hence lies the conundrum.

The "flu continuum" gave little reprieve during the year 2009. It's existence is not designated by man-made seasons, but on it's ability to come back time after time, thereby negating a beginning and end. The question might be changed to, "Have we reached the peak for this session, or is class still in?"

 

[JimO]

Re: Have We Peaked (in the US), Or Is Class Still In Session?

It think Weeks 9 and 10 will be somewhat slow in terms of %ILI and numbers of positive flu cases. Many states will appear to have peaked with the typical pattern. What we need to watch for is increasing percentage positives for pH1N1, upticks in hospitalizations, or sudden flu deaths (rapid onset of pneumonia or multiple organ failure) reported in the media. If pH1N1 is going to cause the kinds of problems it caused in the UK, then we might see double peaks in many states.

I noted that the CDC is asking the states to provide the immunization status associated with samples sent for isolate testing. Perhaps they are concerned about pH1N1 vaccine escape?