Common features of 2009 H1N1 influenza pandemic in different parts of the world revealed by log-log plot of the cumulative numbers of infected and deceased cases.

The log-log plot of the cumulative numbers of infected and deceased cases through the progress of the 2009 H1N1 pandemic gave a relation given by the equation logY = klogX – klogN0, where Y is the cumulative number of infected cases, X the cumulative number of deaths, k the coefficient representing the slope of the curve, and N0 the value of X when the curve crosses the X axis (1). The analysis was made with the data obtained up to July 6, 2009, when the epidemic was limited almost solely to the American continent and mortality on other continents was rare. Since then, the influenza pandemic has spread all over the world. An overwhelming number of new infections made the laboratory testing of all the suspected patients no longer practicable. Reporting of all infected cases was discontinued in many countries, including Japan. Currently, the WHO website gives data only by region, not by country. This paper reports on a further analysis made of the influenza pandemic using the data updated up to November 22, 2009 (http://www. who.int/csr/disease/swineflu/updates/en/index.html; http:// www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou04/ rireki/091228-03.html; http://idsc.nih.go.jp/disease/swine_ influenza/index.html). Fig. 1 shows the log-log plot of the cumulative numbers of laboratory confirmed cases versus deceased cases for WHO Regional Offices except for the Americas (AMRO). The slope of the curve was almost the same, k = 1.7 for Africa (AFRO), South-East Asia (SEARO), and the Eastern-Mediterranean (EMRO), and k = 1.8 for Europe (EURO) and the Western Pacific (WPRO). N0 was about 600 for AFRO, EMRO, and SEARO, and 5,000 for EURO and WPRO. The curves of EURO and WPRO had a breakpoint near (X, Y) = (60,000, 300). The log-log plot for Japan of the estimated cumulative number of infected cases (not laboratory-confirmed cases) versus the cumulative number of deceased cases had a breakpoint near (X, Y) = (1,000,000, 20) after a short initial steep rise with k = 2 and N0 = 300,000. For all of WPRO, EURO, and Japan, after the break, slope k of the curve was about 0.8–0.9 (about 0.9–1.0 after reset at break point; here, “reset” means that the cumulative number before the reset date was subtracted from all the subsequent cumulative numbers). Fig. 2 shows the log-log plot of the cumulative numbers of