Risk factors for pertussis among children hospitalized for pertussis during 2016–2017, in Guizhou Province of China: a case-control study

Aim Pertussis is a respiratory tract infection, the vaccine for which was introduced in the Expanded Programme on Immunization (EPI) in Guizhou Province of China (hereafter referred as Guizhou) in the 1980s. This vaccine rapidly decreased incidence rates of pertussis in the province, however, despite the wide high coverage of the diphtheria, tetanus and acellular pertussis (DTaP) combined vaccine, there has been a resurgence of pertussis since 2014. Even with this recent increase in disease transmission, risk factors for pertussis infection have not been evaluated in Guizhou. We aimed to provide information on pertussis risk factors and insight on designing targeted pertussis control policies and measures through this study. Methods A 1∶2 matched retrospective case-control study was conducted between 2016 and 2017, involving infants and children younger than 6 years old and parents of the participants. The enrolled cases included clinical and laboratory confirmed pertussis cases according to the WHO-recommended pertussis definition. Controls were selected from children in the same neighborhood who were not diagnosed with pertussis prior to our investigation and did not exhibit any clinical manifestations of pertussis. Results The household size [Matched odds ratio (ORm) = 1.4, 95% confidence interval (CI): 1.1–1.7] and household members with antecedent cough (ORm = 3.6, 95% CI: 1.8–7.2) were significantly associated with their child’s pertussis onset. The parents’ occupations were significantly associated with their child’s pertussis onset (ORm = 9.4, 95% CI: 1.6–54.8, for mother side; ORm = 4.5, 95% CI: 1.2–16.5, for father side), when they worked in the business and/or service industry. Having family members with a history of cough was an independent risk factor for pertussis [Adjusted odds ratio (AOR) = 43.6, 95% CI: 2.7–694.0]. Besides, the parents' demographic characteristics and DTaP doses were not found to be independent factors. Conclusion Household exposure is an important risk factor for pertussis infection in infants and young children and should therefore be considered as a major factor during formulation of pertussis control policies and measures.