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Pandemic influenza has emerged 1-3 times each century. The pandemic in 1918, or the "Spanish flu" was caused by a novel influenza strain which caused the death of 21-50 million people world wide. Descriptions of the epidemic in Iceland give a detailed account on how and when the virus was introduced to the population of Reykjavik, the capital of Iceland, by the crew of two ships, "Botnía"· and "Willemoes" on October 19th 1918. The spread of the illness was extremely rapid and peaked 3 weeks later. It caused significant morbidity and mortality among inhabitants of the southern and western part of Iceland. Within 6 weeks, close to 500 individuals had died, thereof more than 50% in Reykjavik. The attack rate in Reykjavik was at least 63% and the case fatality proportion was close to 2.6%. The age-specific mortality was highest among young children, people 20-40 years of age and the elderly. In addition, pregnant women had extremely poor prognosis (37% case fatality). Attempts to halt the spread of the epidemic to the northern and eastern parts of the island were successful. By indentifying the individuals who died from the Spanish flu using historical data, it has recently been shown that genetic factors probably did not play a major role in the pathogenesis of fatal cases. These historical data can be used to assist in planning for new pandemics of influenza, which are believed to be inevitable.

 

Figure 1. Children and hospital staff during the Spanish flu epidemic in Reykjavik. The photograph is probably taken at the Children´s elementary school in downtown Reykjvaik, which was temporarily transformed into a hospital. The first patients were admitted on November 11th 1918. Overall, 107 patients were admitted to this hospital for medical care and 35 of them died (14). Name of photographer unknown. This picture was obtained from Reykjavik photographic archives.

Figure 2. Death announcements in Morgunblaðið, on November 17th 1918, page 3. Reproduced from Morgunblaðið, with permission from the publisher.

Figure 3. Distribution of the Spanish flu in Iceland. The residents of Southern and Western parts, along with the West fjords comprised 64% of all inhabitants of the country in 1918. In general, the illness spread within the shaded area, but smaller communities within the area were not affected, such as the Snaefellsnes peninsula. The absolute number of deaths for each community is shown on the map, with percentage of residents killed by the Spanish flu shown in parentheses. Communities with fewer than 5 deaths from the flu are omitted. The Northern and Eastern parts of the island were placed under self-imposed quarantine at sites A (Holtavörðuheiði) and B (Jökulsá á Sólheimasandi), which prevented the spread of the epidemic to the Northern and Eastern parts of the country. The figure is based on data from (16).

Figure 4. Escalation of the Spanish flu in Reykjavik, according to data from Thordur Thoroddsen (15). The number of new influenza cases, diagnosed by him is shown according to dates of diagnosis. The illness was imported on October 19th. Dr. Thoroddsen saw his first patient on October 28th and subsequently the number of new cases escalated rapidly until mid-November. This was followed by a similar, fairly rapid decline over the ensuing 3 weeks. These data can be used to calculate the basic reproduction rate of the 1918 virus (12).

Figure 5. Age distribution of fatal cases in Iceland (A). Age-specific mortality of patients (B). The data is based on calculations for a 42-day period, October 26th-December 6th 1918. As shown, children 0-4 years, young people 30-34 years of age and the elderly were hardest hit. The graphs are based on data previously published in (12), with slight modifications.

Figure 6. Age distribution of patients diagnosed with pneumonia, according to Dr. Thoroddsen (15). According to his description, 292 of his 1232 patients contracted pneumonia, or 23.7%.

Figure 7. Number of live births in Iceland/1000 inhabitants/year during the period 1915-1923. As shown, the average number was 26.5-28 children for all years except for 1919, when this number fell to 23.3. It can be argued that this drop could be due to high number of miscarriages among pregnant women during the fall of 1918. The graph is based on data from Statistics Iceland.