Transmissibility of acute haemorrhagic conjunctivitis in small-scale outbreaks in Hunan Province, China

Abstract

Acute haemorrhagic conjunctivitis (AHC) outbreaks are reported frequently in China. However, the transmissibility of AHC remains unclear. This study aimed to calculate the transmissibility of the disease with and without interventions. An AHC outbreak dataset from January 2007 to December 2016 in different schools was built in Hunan Province. A Susceptible-Infectious-Recovered (SIR) model was adopted to calculate the effective reproduction number (R_eff) of AHC. R_eff was divided into two parts (R_unc and R_con) where R_unc and R_con represent the uncontrolled and controlled R_eff , respectively. Based on R_unc and R_con, an index of effectiveness of countermeasures (I_eff) was developed to assess the effectiveness of countermeasures in each outbreak. During the study period, 34 AHC outbreaks were reported in 20 counties of 9 cities in Hunan Province, with a mean total attack rate of 7.04% (95% CI: 4.97-9.11%). The mean R_unc of AHC outbreaks was 8.28 (95% CI: 6.46-10.11). No significance of R_unc was observed between rural and urban areas (t = -1.296, P = 0.205), among college, secondary, and primary schools (F = 0.890, P = 0.459), different levels of school population (F = 0.738, P = 0.538), and different number of index cases (F = 1.749, P = 0.180). The most commonly implemented countermeasures were case isolation, treatment, and health education, followed by environment disinfection, symptom surveillance, and school closure. Social distance, prophylaxis, and stopping eye exercises temporary were implemented occasionally. The mean value of R_con was 0.16 (range: 0.00-1.50). The mean value of I_eff was 97.16% (range: 71.44-100.00%). The transmissibility of AHC is high in small-scale outbreaks in China. Case isolation, treatment, and health education are the common countermeasures for controlling the disease.

Figure 1

Spatial distribution of 34 reported AHC outbreaks, TAR, and R_unc in Hunan Province. (A) Number of outbreaks; (B) mean value of TAR in each county; (C) mean value of R_unc in each county.

Figure 2

Temporal distribution of 34 AHC outbreaks in Hunan Province from 2007 to 2016.

Figure 3

The epidemic curves of 32 outbreaks selected for calculating R_unc and R_con in Hunan Province, China.

Figure 4

The example for curve fitting to calculate R_unc and R_con using in a small-scale outbreak in school. In this example, epidemic curve was divided into two parts (without and with intervention) according to the date when the interventions were implemented. The R_eff of AHC, which was denoted as R_unc during the part without intervention and was denoted as R_con after the interventions implemented, was assumed to be different between the two parts.