THE THIN WHITE LINE: the history of a future avian influenza pandemic

Chapter 2: State of Emergency

Like the Spanish Flu at its worst

By October 26, the epidemic had been developing for about a week in Calgary and began a major assault on the health system. Public health officials now estimate that 18,000 people in the Calgary Health Region, which constituted about 1.2 million people served by five urban and eight rural hospitals, caught the Avian Flu by this time.
About half of these people experienced no symptoms, although they could infect others. The other half sought outpatient care—through a visit to a clinic or family physician—or hospitalization. Among this segment, nine out of 10 people faced the usual three- to five-day crushing illness that anybody with seasonal flu suffered, albeit even harsher, more painful and sometimes accompanied by nosebleeds. Ten percent developed pneumonia or other complications and required hospitalization, and about 12.5 percent of these (or 1.25 percent of all clinically ill cases) died, sometimes within days; the highest mortality occurred among healthy 20- to 40-year-olds.

Table 2-1. Progress of the epidemic and its estimated impact on the Calgary Regional Health Authority as of October 26, considered the end of its first full week.(25) For more information, see the Appendix.

	Week 1
Clinically ill	18,020
Hospital admissions	1,802
Hospital acute care bed capacity	2,105
Requiring acute care beds	1,397
Bed demand as % capacity	66%
Requiring ICU beds	270
ICU bed capacity	57
ICU demand as % capacity	474%
Requiring ventilators	135
Ventilator bed capacity	186
Ventilator demand as % capacity	73%
Total mortality (1.25% of clinically ill)	225

Already, just one week into what would be a 10-week epidemic, the hospitals reported a flood of cases.

    Historically, pandemic influenza strains emerge roughly every 11 to 44 years. One out of four appears to be particularly virulent. Looking at the twentieth century, three major pandemic events occurred—one severe, and two relatively mild.
    The Spanish Flu, considered a severe pandemic flu, killed 40 to 100 million worldwide. The Asian Flu of 1957, considered a moderate pandemic flu, killed an estimated two million, and the Hong Kong Flu of 1968, also considered moderate or even mild, killed about a million.
    Pandemics historically occur in one, two or three waves, each about six to eight weeks in duration for a given region, and spaced two to nine months apart. In a large country such as Canada, the epidemic may take three to six months until it peaks and cases start their decline to zero. The first wave is often mild because the virus may be still learning how to adapt to humans. By the second wave, the virus has typically learned, through repeated mutations, how to spread rapidly among its new human hosts, while becoming more virulent. The third wave, if it occurs, is also considered deadly, although by this point most of the population, or an estimated seven out of 10 people, will have already caught the disease. After the second or third wave, novel influenza viruses may evolve the other way, becoming milder so as to reach an accommodation with humans. The infamous Spanish Flu, in fact, is believed to be circulating even today as common seasonal flu H1N1.
    Out of the gate, the Avian Flu of 2012 behaved like the Spanish Flu of 1918-19 at its worst. It killed 2.5 percent of those who became clinically ill from it. And it spread rapidly through the population.(26)