Helmet use among motorcycle riders in Ho Chi Minh City, Vietnam: results of a five-year repeated cross-sectional study

Objective: In Vietnam, motorcycle riders comprise about three-quarters of road traffic fatalities, the most common cause of which is head injuries that can be prevented by wearing a helmet. This study aims to assess helmet-wearing behaviors in Ho Chi Minh City, the largest city in Vietnam. Methods: Eight rounds of observational studies were conducted in six randomly selected locations between July 2015 and April 2019. Given the multinomial nature of the outcome measure (not wearing a helmet; wearing a substandard helmet; wearing an unstrapped standard helmet; wearing a strapped standard helmet), a multinomial model was developed to estimate the level and trend of helmet use and identify the related individual and environmental factors. Findings: A total of 479,892 motorcycle riders were observed, over 90 % of whom were wearing helmets (range over the eight rounds: 92.5 %–96.0 %). However, the prevalence of correct helmet use (defined as wearing a strapped standard helmet) gradually declined from 80.8 % in round 1–55.6 % in round 8. Results from a multinomial model showed the probability of wearing a strapped standard helmet had declined by 22.4 percentage points from round 3 to round 8 while holding other factors constant (95 % CI: 21.8–23.0). The prevalence of correct use is 11.3 percentage points higher for adults than for children (95 % CI: 10.5–12.1). During the same period, unstrapped standard helmet use increased by 24.5 percentage points (95 % CI: 24.1–24.9); substandard helmet use declined but remained high. Conclusion: The upward trend of incorrect helmet wearing behaviors and wearing substandard helmets sends a rallying call for multisectoral interventions.