Efficacy of compartmentalization in controlling an adenovirus type 54 keratoconjunctivitis outbreak on Oki Island, Japan

Abstract

Purpose: To analyze the epidemiologic characteristics of an outbreak of human adenovirus type 54 (HAdV-54) on Oki Island, Shimane Prefecture, Japan, in 2017 and to assess the effectiveness of a compartmentalization method in controlling the incidence and spread.

Study design: Retrospective cohort study.

Methods: The infection was diagnosed in 136 individuals, and typing was confirmed by PCR and direct sequencing. The epidemiologic characteristics of the disease including the infection rate, incubation period, and basic reproductive number (R₀), ie, number of cases directly infected by an infectious patient during the course of the disease, were investigated. The effectiveness of compartmentalization for infection control was determined by simulating the outbreak using the Susceptible-Exposed-Infectious-Recovered (SEIR) model.

Results: The majority of the HAdV-54-infected individuals were the children of 3 nursery schools (A, B, and C) and their parents on Oki Island. The infection rates in the 3 schools were 13.2%, 16.9%, and 17.2%, respectively. The one class of school B without the index case was initially compartmentalized, and the infection rate in this compartment was 0%. The incubation period was calculated to be 9.3 ± 3.5 days, and the disease duration, 13.0 ± 5.4 days. The R₀ was 1.43. Using these parameters, a SEIR model was constructed. The SEIR model well predicted the daily incidence of infection and indicated that the compartmentalization method provides effective reduction in the incidence of the infection, with much earlier control.

Conclusions: The compartmentalization method is effective to control HAdV-54 outbreaks.

Keywords: Adenovirus type 54; Basic reproductive number; Compartmentalization; Epidemic keratoconjunctivitis; Susceptible-exposed-infectious-recovered model.

Fig. 1

Demographics of the outbreak of adenovirus type 54 keratoconjunctivitis on Oki Island in Shimane Prefecture, Japan. a Map of the locations of 8 nursery schools on Oki Island. The square area surrounded by the broken line is the area of map b. b The circled area within the broken line is the area within 2 km of Saigo Port (filled square). There are 4 Schools, A, B, C and D, in the circled area. The numbers indicate the infected/total number of children. The arrow indicates the infection route and outbreak spread from school B

Fig. 2

Outbreak of adenovirus type 54 epidemic keratoconjunctivitis on Oki Island. a The number of newly infected individuals in the entire population peaked in early November 2017. b The age distribution was bimodal: ≤ 5 and 30–35 years

Fig. 3

Time course changes of the patients, nursery school children and their family members. The outbreak began in school B, and then in schools C and A. The blue bar indicates the number of nursery school children infected in the nursery schools. The red bar indicates the number of family members of the infected children of the nursery schools. The findings suggested that most members of the infected families were infected by children infected at the nursery schools

Fig. 4

Nursery school-based cumulative infection and prediction using the SEIR model. a Flow diagram of the SEIR model consisting of 4 compartments: the susceptible (S), exposed (E), infectious (I), and recovered (R) individuals. $\beta$: preintervention transmission rate;$\gamma$: 1/mean infectious period;$a$: 1/mean incubation period. The 3 graphs below represent school A (b), B2 class of school B (c), and school C (d). The bar chart indicates the actual cumulative number of infections. The line chart indicates the predicted cumulative number of infections according to the SEIR model using an R₀ of 1.43 and an incubation period of 9 days. The highest cumulative number of infections was observed for B2 class of school B (c), where the number of index cases was 3, as compared with 1 each for schools A (b) and C (d)

Fig. 5

Effect of compartmentalization on cumulative infection rate predicted by the SEIR model. a The cumulative infection rate of B2 class of school B was calculated using the SEIR model. The cumulative infection rate without compartmentalization was 20.9% (solid line). The gray line indicates the results in the case that B2 class of school B was compartmentalized for 1 compartment with 1 exposed and the other with 2 exposed but asymptomatic children. The dotted line indicates the effective compartmentalization by which B2 class of school B was divided into 1 compartment with only unexposed children and the other with 3 exposed but asymptomatic children. The cumulative infection rate was reduced to 13.9%. b Simulation of cumulative infection in different compartments of 14,000 islanders by use of the SEIR model. The number of indices is set to 10. The largest compartment was 14,000. When the compartment size was reduced to 5000, 1000, 500, 100, and 50, the cumulative number of infections was significantly reduced, and an earlier ending of infection (plateau) was observed. The ordinary differential equation of the SEIR model was solved using Online Resource 1 Code (txt file and ipynb file)