2014.ISDS.Abstracts.Final.pdf


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ISDS 2014 Conference Abstracts

Inconsistency of Timeliness in a Chief Complaint-Based
Syndromic Surveillance System During Two Influenza
Epidemic Seasons

Tao Tao*1, Qi Zhao1, Jun Zong2, Xue Li3, Vinod Diwan4 and Biao Xu1

1School of Public Health, Fudan University, Shanghai, China; 2Jiangxi CDC, Nanchang, China; 3Future Position X, Gävle, Sweden; 
4Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden

Objective
To study and compare the timeliness of syndromic surveillance 

system for the early warning of infectious diseases among different 
epidemic seasons.

Introduction
Syndromic surveillance system has been developed and 

implemented all over the world, and many studies showed that 
syndromic data sources had improved timeliness towards traditional 
surveillance method in the early warning of some infectious disease 
epidemics. However, owing to the uncertainties of disease epidemic 
features, clinical manifestations and population behaviors, the early 
warning timeliness of syndromic data sources might change across 
time and population, and few studies had explored their consistency 
in different epidemic periods of infectious diseases.

Methods
We evaluated the timeliness of a chief complaint-based syndromic 

surveillance system established in two rural counties of Jiangxi 
Province, China, towards seasonal influenza epidemics. Weekly 
number of influenza-like illness (ILI) patients counted from 
syndromic surveillance system was compared with the weekly 
influenza virus positive rate (VPR) data collected from National 
Influenza Surveillance Network in Jiangxi Province using cross 
correlation method. Timeliness was defined as the lead weeks of ILI 
data towards VPR data when two data sources reached maximum 
correlation. Daily data check and quarterly field data quality control 
was conducted to ensure the correctness and completeness of data in 
syndromic surveillance system.

Results
From 18th week 2012 to 52nd week 2013, there were two influenza 

epidemic seasons in surveillance areas according to the VPR data 
from National Influenza Surveillance Network. Apparent correlation 
could be observed between ILI and VPR curves, and in some 
periods the ILI peaks occurred earlier than VPR peaks (Figure 1). 
Cross correlation study showed that in Epidemic Season 1, the 
subgroups of ILI data had 0~5 weeks’timeliness towards VPR data, 
with correlation coefficients between 0.52~0.84. ILI reported from 
upper-level health facilities (county and township hospitals), younger 
patient groups (3-17 years) had higher timeliness than ILI reported 
from village health stations, elder patient groups (18- years) (Table 
1). The situation in Epidemic Season 2 were quite different that the 
correlations between ILI subgroups and VPR data were generally 
weaker than that in Epidemic Season 1, and some ILI subgroups even 
presented 1~5 weeks’delays towards VPR data. ILI reported from 
village health station, elder patient groups (18- years) had better 
timeliness than that from upper-level health facilities, younger patient 
groups (0-17 years) (Table 2). Lab data showed that the dominant 
influenza strains were different in two epidemic seasons.

Conclusions
The inconsistency of timeliness in syndromic surveillance system 

might be attributed to the differences in dominant strains, clinical 
manifestations of influenza, population age groups affected, and 
health seeking behaviors of influenza patients in two epidemic 
seasons. Further exploring the causes of these phenomena could help 
public health professionals select most timely data sources for the 
early warning of influenza epidemics in rural China.

Keywords
Timeliness; Syndromic surveillance; Epidemic season

*Tao Tao

E-mail: ttsuper2000@hotmail.com    

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org * (1):e92, 201