Application of zero-inflated negative binomial model to study the pattern of Ascaris lumbricoides and hookworm re-infection

Objective Use zero-inflated negative binomial model for modeling the pattern of Ascoris lumbricoides and hookworm re-infection.Methods Field survey was carried out in three villages:Qiuchang in Yibin City of Sichuan Province,Tangnan in Jinxian County of Jiangxi Province,and Sanhe in Yueyang County of Hunan Province.The survey consisted of baseline stool examination and treatment,re-examination after one month and one year,and questionnaire survey.Zero-inflated negative binomial model was applied to fit the egg count data collected after one year,meanwhile,the risk factors for the re-infection occurrence and intensity were evaluated.Results Totally 374 subjects were recruited in the survey after one year.The prevalences of Ascaris lumbricoides and hookworm at baseline 38.08％(139/365) and 39.17％(141/360).The re-infection rates of Ascaris lumbricoides and hookworm one year after treatment were 15.89％ (58/365) and 8.89％ (32/360),respectively.A.lumbricoides model showed:the higher infection intensity before treatment,the higher risk of re-infection occurrence(OR=1.94,95％CI:1.33～2.81),high level of household electrical appliances and not drinking un-boiled water were protective factors.The risk of re-infection in age group 15～44 years and 45～64 years was lower than that in group 5～14 years significantly.The higher infection intensity before treatment,the higher risk of high re-infection intensity after treatment (OR=1.56,95％CI:1.10～2.23).Compared to age group 5～14 years,15～44 years and 65～70 years had low risk of getting high re-infection intensity.Not drinking unboiled water was also a protective factor for acquiring high intensity.Hookworm model showed:the higher infection intensity before treatment,the higher risk of re-infection occurrence (OR =3.97,95％CI:2.07～7.60),living in brick house opposed to adobe house was protective factor for re-infection.Compared to age group 5～14 years,the other 3 age groups had higher risk of getting high re-infection intensity,with age group 45～64 the highest.People receiving high school education had lower risk of acquiring high re-infection intensity,relative to illiterate or semi-illiterate people.Conclusion Zero-inflated negative binomial model is the optimal statistical model for fitting Ascaris lumbricoides and hookworm egg count data.This study proved the existence of predisposition phenomenon in the process of re-infection.The occurrence and intensity of re-infection were related with infection intensity before treatment,demographic,socio-economic,environmental and behavioral factors. Key words: Ascaris lumbricoides;  Hookworm;  Re-infection;  Zero-inflated;  Negative binomial;  Predisposition