Children Learning About Secondhand Smoke (CLASS III): a protocol for a cluster randomised controlled trial of a school-based smoke-free intervention in Bangladesh and Pakistan.

Introduction: Secondhand smoke (SHS) exposure is a major cause of premature death and disease, especially among children. Children in economically developing countries are particularly affected as smoke-free laws are typically only partially implemented and private homes and cars remain a key source of SHS exposure. Currently, firm conclusions cannot be drawn from the available evidence on the effectiveness of non-legislative interventions designed to protect children from SHS exposure. Following the success of two feasibility studies and a pilot trial, we plan to evaluate a school-based approach to protect children from SHS exposure in Bangladesh and Pakistan-countries with a strong commitment to smoke-free environments but with high levels of SHS exposure in children. We will conduct a two-arm cluster randomised controlled trial in Bangladesh and Pakistan to assess the effectiveness and cost effectiveness of a school-based smoke-free intervention (SFI) in reducing children's exposure to SHS and the frequency and severity of respiratory symptoms.

Methods And Analysis: We plan to recruit 68 randomly selected schools from two cities-Dhaka in Bangladesh and Karachi in Pakistan. From each school, we will recruit approximately 40 students in a year (9-12 years old) with a total of 2720 children. Half of the schools will be randomly allocated to the intervention arm receiving SFI and the other half will receive usual education. Salivary cotinine concentration-a highly sensitive and specific biomarker of SHS exposure-is the primary outcome, which will be measured at month 3 post-randomisation. Secondary outcomes will include frequency and severity of respiratory symptoms, healthcare contacts, school absenteeism, smoking uptake and quality of life. Embedded economic and process evaluations will also be conducted.

Ethics And Dissemination: The trial has received ethics approval from the Research Governance Committee at the University of York. Approvals have also been obtained from Bangladesh Medical Research Council and Pakistan Health Research Council. If SFI is found effective, we will use a variety of channels to share our findings with both academic and non-academic audiences. We will work with the education departments in Bangladesh and Pakistan and advocate for including SFI within the curriculum.

Trial Registration Number: ISRCTN28878365.