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H1N1 (Swine Flu): INFLUENZA – UNPREDICTIBLE H1N1

August 13, 2009

Two interesting articles caught my attention over the past two days – both about the unpredictable nature of influenza…it turns out the crystal ball might be a bit cloudy!

LOOKING TO THE PAST TO PREDICT THE FUTURE

We often look to the past in a way of predicting the future – it is one thing that can help us in forecasting illness.  A commonly held belief that severe influenza pandemics are preceded by a milder wave of illness arose because some accounts of the devastating flu pandemic of 1918-19 suggested that it might have followed such a pattern.  This long held belief might just be biting the dust – two scientists from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, report that the existing data is insufficient to conclude decisively that the 1918-19 pandemic was presaged by a mild, so-called spring wave, or that the responsible virus had increased in lethality between the beginning and end of 1918.

1918 Pandemic Waves

1918 Pandemic Waves

Furthermore, their analysis of 14 global or regional influenza epidemics during the past 500 years reveals no consistent pattern of wave-like surges of disease prior to the major outbreaks, but does point to a great diversity of severity among those pandemics. So much for history!

The researchers noted that the two other flu pandemics of the 20th century, those of 1957 and 1968, generally showed no more than a single seasonal recurrence; and in each case, the causative virus did not become significantly more pathogenic over the early years of its circulation.

Milder First Wave?  Not really?

What is the net-net?  The variable track record of past flu pandemics makes predicting the future course of H1N1 difficult. They also noted that the characteristics of the novel H1N1 virus, such as its modest transmission efficiency, and the possibility that some people have a degree of pre-existing immunity give cause to hope for a more sluggish pandemic course and fewer deaths than in many past pandemics.

They concluded however that robust, ongoing efforts to meet the return of 2009 H1N1 virus with vaccines and other measures are essential responses to a notoriously unpredictable virus. In closing, the authors conclude, paraphrasing Danish philosopher Soren Kierkegaard, “influenza epidemics are lived forward and understood backward.”

I like that quote

DM Morens and JK Taubenberger. Understanding influenza backward. Journal of the American Medical Association 302: 679-80. DOI: 10.1001/jama.302.6.679 (2009).

National Institute of Allergy and Infectious Diseases (NIAID) http://www3.niaid.nih.gov/news/newsreleases/2009/fluPredictors.htm

LESSONS IN FIGHTING H1N1

The NY Times had a great article this week by Dr. Lawrence Altman.  It pointed again to the illusive nature of the virus and the weakness in our collective response.

One of the weaknesses is that despite years of planning it is evident that the infrastructure of the health departments in many countries, including the United States, is inadequate (in varying degrees) to deal with the sudden appearance of a new strain of influenza. Also, the number of beds in hospital intensive-care units and emergency rooms is limited, as is equipment like mechanical respirators to help patients breathe when the virus attacks the lungs.

Officials and experts say they have learned a lot about human swine influenza. But relatively little of that information, including periodic summaries of what has been learned since the beginning of the pandemic, has been reported and published. Some experts said researchers were waiting to publish in journals, which can take months or longer. Journals impose severe penalties for disclosing information before publication, although they say they exempt matters of public health importance. Whatever the reason, delays in reporting such information can hamper plans for public health responses.

Where’s the fever? Diarrhea?

Not all cases present with fever

Not all cases present with fever

The standard definition of influenza includes a fever. But an odd feature of the new virus is the lack of fever in a significant proportion of documented cases, even after some patients become seriously ill. In Chile, it was about half, in Mexico City about a third and elsewhere, less. Analysis of data from specimens yet to be tested may shed light on how often infected individuals who have no fever spread the virus. So absence of fever among substantial proportions of patients, when fever is specified in the definition, can cause serious underestimation of case totals.

Diarrhea is a symptom that appears to be occurring in a larger percentage of cases (25% on average) than in seasonal influenza, giving clear reason to reinforce the importance of frequent hand washing.

The course of illness can become life-threatening in just a few hours among patients who had shown only mild symptoms, The article noted that “doctors know little about what treatment works in severe cases. ”Mexican and Argentinean doctors have noted that cases peak over a four-week period, drop substantially over succeeding weeks to very low numbers, and then pop up elsewhere in the countries,

Two more unusual features of the new virus is that pregnancy, particularly in the third trimester, and obesity appear to increase the risk for complications of the infection.  Be alert for these in the fall.

NY Times – http://www.nytimes.com/2009/08/11/health/11docs.html?tntemail0=y&_r=1&emc=tnt&pagewanted=print

Crystal Ball #3

So what is the net-net of all of this – be ready for just about anything – from a mild wave to one more severe.  I think we need a new crystal ball!

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