Page 101 - Timeliness of Infectious Disease Notification & Response Systems - Corien Swaan

Quantifying reporting timeliness to improve outbreak control 99
outbreak control condition is R2 x PIR2<1, assuming index cases are reported too late to stop any secondary infection (i.e., PIR1=1 always). The upper outbreak control condition R x PIR2<1, which is the most relaxed condition, assumes an extreme situation that index cases have not caused more infections than secondary cases (PIR1=PIR2). In prac- tice the outbreak control condition lies in between these 2 conditions. Diseases that lie in the outbreak control areas are those for which reporting speed is timely enough to allow outbreak control. PIR 2, expected proportion of new infections caused by secon-
dary cases before index case is notified; R, reproduction number. Table 2. Effects of reducing reporting delays, by disease*.
Disease
Current PIR1
(PIR1 at symptom onset)
Current PIR2
(PIR2 at symptom onset)
PIR2 reduction ratio by reducing delay in 1 d
Reporting delay median needed for PIR2=1/R
Reporting delay median needed for PIR2=1/R2
Underreporting beyond which outbreak control is not possible
Reduction of vaccination coverage for herd immunity
Hepatitis A
0.818 (0.480)
0.145 (0.019)
9.7% 17 d 8d 29%
70%
Hepatitis B
0.907 (0.810)
0.456 (0.320)
1.5% 42 d 1d 1.5%
64%
Measles Mumps
0.947 0.901 (0.495) (0.574)
0.423 0.273 (0.006) (0.005)
12.6% 13.5% 5d 8d 2d 3d 12% 18%
8% 20%
Pertussis Shigellosis
0.948 0.960 (0.322) (0.230)
0.817 0.836 (0.067) (0.056)
0.7% 2.4%
4.5 d 3d
Not pos- 1d sible
12% 25% 2% 4%
* PIR values at symptom onset show a theoretical minimum, achievable by stopping transmission instantly at symptom onset. PIR1, proportion of expected infections pro- duced by an index case; PIR2 proportion of expected infections produced by each se- condary case produced by a reported index case.
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