A Journey Through The World of Pandemic Influenza

Pandemic Mitigation II

Last night I addressed pandemic mitigation from a general, community level (here), tonight I would like to discuss the issue on an individual level.

There are 300 million +/- people in the US and according to the 2000 US Census 69% percent of us live in areas that have a population of 50,000 or more, in 3,629 urban areas. For a breakdown of percentage by state see here. I was quite surprised to learn that my state (SC) is the least urban density in the nation—a good thing in a moderate to severe pandemic.

 

Using official estimates of what could be anticipated for a severe pandemic a 30% CAR (clinical attack rate) and 2% CFR (case fatality ratio) we can glimpse into our crystal balls and see what might be in store for our states and our cities.

For my area, the city, (Charleston), has 425,000+/- residents. That would mean that my city would see roughly 127,500 PanFlu illnesses and 2,550 illnesses directly attributed to those illnesses. Were I to figure it for the entire area, known locally as The Tri-County the figures are as follows: 603,500 residents, 181,050 PanFlu illnesses, and 3,621 PanFlu deaths.

Of course, we have no way of knowing what the CAR/CFR of the next pandemic will be, should one occur, but currently H5N1 has a cumulative CFR of just over 60%. Assuming a pandemic of H5N1 for my purposes here, a drop of 90% in the current CFR would still leave us dealing with a CFR of 6%, and that would translate to 7,650 deaths for my city and 10,863 for my entire area. When I type "deaths" and you read "deaths", it is important to remember that those numbers represent people: men, women and children. In the case of the figures I quoted those are my neighbors, co-workers, friends and family members.

 

I went through all the effort to type all of the above out because I feel it is important to be crystal clear about what I am addressing in this entry, what we, as individuals, can do to reduce our chances of being included in our community's statistics.

 

So, what can we reasonably do to protect ourselves? Until we have a vaccine released to our demographic/cohort, (for a draft guidance of vaccine priority sees here), we will have to rely on Non-pharmaceutical Interventions—NPI's.

• Keep your children out of school no matter what your school's official policy is. Not only are children the most efficient spreaders of influenza, schools are over crowed and perfect amplification points for any infectious disease.
• Maintaining social distancing: 3 feet or more.
• Frequent hand washing
• Avoiding touching our faces
• Avoiding touching common surfaces: anything someone else may have touched. Both influenza A and B viruses survived for 24-48 hr on hard, nonporous surfaces such as stainless steel and plastic but survived for less than 8-12 hr on cloth, paper, and tissues. Measurable quantities of influenza A virus were transferred from stainless steel surfaces to hands for 24 hr and from tissues to hands for up to 15 min. Virus survived on hands for up to 5 min after transfer from the environmental surfaces. J Infect Dis. 1982 Jul;146(1):47-51
• Use alcohol based hand sanitizer liquid or gel any time you touch a common surface
• Work from home if at all possible
• Stay home if possible (known as SIP or Shelter in Place by Flubies)
• Minimize physical contact
• Wear a mask: N95, surgical, homemade (in order of effectiveness and difficulty of obtaining during a pandemic) My blog entry for the CDC's offering on a homemade mask here, and a discussion thread about masks, as well as tossing around ideas on mask workarounds in general on P4P here.
• Stay home if you become ill with any illness; you will not know if it is PanFlu or not for a day or three and you do not want to be out spreading germs.

   

 

Will doing these things guarantee you will not get PanFlu should we suffer a pandemic? I cannot give you a definitive yes to that question, but they will reduce your chances of becoming infected, and short of an effective vaccine, that is probably the best we will be able to manage—reduce our chances of becoming infected. An aside: For the latest release on the steps and timeline involved in producing a PanFlu vaccine see the WHO's PDF here; the pandemic is likely to be over before we have an effective vaccine.

 

 

Here's hoping none of us end up as a PanFlu statistic.

 

SZ

Basics: Pandemic Severity

I often use the phrase "moderate to severe PanFlu", when I do so I generally use my own criteria for what will constitute severe.

Generally I qualify any CFR at 5% or less as a moderate pandemic, where the CDC has settled on the criteria below 2%.

And just for clarity's sake I hold the opinion that a CFR above 15% would be catastrophic to everyone and everything.

I should probably adjust my phrasing but I won't, I am used to the mental constructs that have informed my thinking up to this point.

Early this year the CDC (Centers for Disease Control and Prevention) developed and published a way to judge pandemics, in the pre-pandemic planning stage, by severity, assigning categories reminiscent of hurricane strength classifications.

The model assumes that 30% of the overall population will get the pandemic strain of the virus, although different age groups and population centers may experience significant differences in the percentages, both overall and in the specific age groups.

Age groups can be thought of as preschoolers, elementary school children, students in upper grades, working adults, older adults, and finally, the elderly.

Official assumptions seem to be that the age group that will experience the highest level of illness is the younger children, picked up in daycare centers and school.

The percentage of the population expected to become ill is termed the Case Attack Rate, sometimes stated as the acronym CAR.

The numbers of those ill who are expected (statistically) to die are the Case Fatality Ratio (CFR).

From Wikipedia:

The pandemic severity index levels are:

• Category 1, CFR of less than 0.1% (example: seasonal flu)
• Category 2, CFR 0.1% to 0.5% (examples: Asian Flu and Hong Kong Flu)
• Category 3, CFR 0.5% to 1%
• Category 4, CFR 1% to 2%
• Category 5, CFR 2% or higher (example: Spanish flu

Recommendations for a response to a flu pandemic were based on the history of the last three major flu pandemics, mathematical models, seasonal flu transmission, and input from experts and citizen focus groups.

It should be noted that the Category 5 on the CDC's pandemic scale has a fatality ratio of 2% or greater. Currently the CFR is just a bit over 60%, both cumulative since 2003, and also if one only includes the cases thus far in 2007. The yearly CFR can, and has, varied from the cumulative CFR, sometimes markedly.

1.8 million deaths in the United States are estimated for a Category 5 pandemic with a CAR of 30% and CFR of 2%. An increase of 1% in the CFR would result in 2.7 million deaths, or an increase of 10% in the CAR would result in 2.4 million deaths.

Each 1/10^th of the total US population translates to 30,000 people. Living, breathing, loving, laughing, men, women, and children, not abstract numbers. Something I fear often gets consigned to oblivion as we toss out numbers, levels, categories, and statistics in our presentimental predictions.

There are other variables that drive the severity or mildness of an influenza pandemic, but I will save them for another day.

Finally, while an influenza pandemic based on the officially sanctioned criteria for severe, 30% CAR and 2% CFR would be bad, it could be a great deal worse. At this time no one knows what the next pandemic will be in terms of pathogen, lethality, or numbers likely to be stricken. The range is wide, from barely above "normal" all the way to atrociously catastrophic. We watch, we analyze, we guess; we plan for the worst and hope to have it prove to have been done in vain.

SZ