Data show that SARS is gradually coming under controlBMJ 2003; 326 doi: https://doi.org/10.1136/bmj.326.7400.1166-b (Published 29 May 2003) Cite this as: BMJ 2003;326:1166
All rapid responses
Parry(1) mentioned the recent rapid increase of SARS infections in Taiwan(2), making it the third worst affected area in the world, and the question whether it is under control. The daily numbers of new SARS cases in Taiwan as reported through June 2 (Figure 1) have declined since mid-May. However, the number can be deceiving. Due to delay caused by incubation time of the infected persons as well as time lag for diagnosis and reporting, there could a subsequent underreporting in the most recent 7 to 10 days.
In order to ascertain the true direction of the epidemic, we make use of the series of cumulative number of SARS cases in Taiwan obtained from the same data set for the period March 12 - May 25 to fit an exponential curve with series autocorrelation in the error structure. The residuals of true values minus the predicted values of the curve fitting are given in Figure 2. From March 12 to April 19 the model fits very well, showing the growth to be exponential. During April 20 - May 13 when a series of hospital outbreaks occurred(3), the data exhibit wild variations and the predicted values consistently underestimate the true values.
Between May 14 and May 25, the consistently downward trend of the real values shows that the increase of the cumulative number of SARS cases is again exponential, albeit at a much slower rate. The stochastic variations during April 20-May 13, caused by a series of breakdown in the health infrastructure, cannot be explained by a simple model. But Figure 2 offers definitive evidence that the growth of the epidemic is back to exponential but slowing down. It is worthwhile to note that while the daily numbers in Figure 1 exhibits peaks around May 11-19, contributed by the last major hospital cluster infections in the South of Taiwan during mid-May, the residuals in Figure 2 readily show a downward trend as early as May 14, indicating that even with the last outbreak in health care setting in the South, control measures have finally started to take effect. However, recent developments in Toronto should serve as a warning for the possible consequence of a single misreporting, lest we let down our guard.
Ying-Hen Hsieh(#) and Cathy Woan-Shu Chen(*)
(#)Department of Applied Mathematics, National Chung Hsing University, Taichung, Taiwan
(*) Department of Statistics, Feng Chia University, Taichung, Taiwan
Correspondence to: Professor Y.-H. Hsieh, Department of Applied Mathematics, National Chung Hsing University, 250 Kuo-Kuang Rd., Taichung, Taiwan 402 (e-mail: email@example.com)
1. Parry J. Data show that SARS is gradually coming under control. BMJ 2003:326:1166.
2. WHO. Update 59 - Report on Guangxi (China) visit, situation in Taiwan, risk of SARS transmission during air travel. (Available at http://www.who.int/csr/sars/archive/2003_05_19/en/.)
3. Hsieh YH. Politics hindering SARS work. Nature May 22, 2003; 423: 381.
Figure 1. Numbers of SARS cases in Taiwan
by onset date (as reported through June2, 2003)
*Data from Center for Disease Control of Taiwan website,available at http://www.cdc.gov.tw/sarsen
Figure 2. The residuals of true values minus the predicted values of the cumulative number of SARS cases as fitted by the exponential model
Competing interests: No competing interests
As suggested by Parry1 the number of SARS cases appears is be
slowing. According to the World Health Organization (WHO)2 as of May 31,
2003 there were 8,360 cases and 764 deaths. This is a change of 138 new
or probable cases and 39 deaths from May 26, 2003, a five-day period. If
the epidemic of SARS follows that of influenza and colds, which include
corona viruses, as spring turns to summer the number of cases will
naturally dissipate. The real test will be if SARS re-emerges next year
with the cold and flu season. This is especially important if a reservoir
is not discovered for the new virus.
As for now, the emergence of summer will have a natural damping of
the disease rates. However, lets not forget this event, in that it may re
-emerge, stronger than ever, during the next winter season.
1. Parry J. Data show that SARS is gradually coming under control.
BMJ 2003: 326: 1166.
2. WHO. Cumulative number of reported probably cases – May 31, 2003,
World Health Organization website, June 1, 2003.
Competing interests: No competing interests