The demographic characteristics of our study population showed a male predominance 123 (86.0%), with a median age of 30 years (23–36 years) and 85% of patients enrolled in this study were the victims of road traffic injury (RTI). This is a similar to the reported trauma burden facing many LMICs, in which, morbidity and mortality from RTIs have taken a sharp rise over the last decade due to rapid urbanization and population growth [16–19]. In this cohort, most of the victims were drivers of motorcycles, famously known as “boda-bodas”, which are local motorcycle taxis used to ferry patients to different parts of the main city. This is a concerning revelation that needs urgent policy and law enforcement to protect the drivers, passengers and pedestrians.

We found that 47% of the injured patients presenting to our ED tested positive for alcohol, 36% tested positive for the use of illicit drugs, and nearly 29% tested positive for both alcohol and illicit drugs. These are very high rates of substance abuse use compared to most of the studies we came across, including the global report on substance abuse in 2014 which reported the prevalence of alcohol and illicit drug use range respectively between 6 to 45% and 2 to 25% [14, 20–22]. In our study, alcohol was the most frequent substance found amongst injured patients (46.9%), followed by marijuana (24.5%), opioids (11.4%), benzodiazepines (9.8%) and amphetamines (2.4%). Marijuana was most prevalent in younger patients (median age of 26 years). Many studies on alcohol and illicit drug use conducted worldwide reported similar results as ours in terms of which substances are most frequently detected in injured patients [22–24]. The high proportion of young males using drugs and alcohol and sustaining injuries in our study is particularly concerning as this is the age group that is expected to be economically productive, and often represent the breadwinner in Tanzanian households [13, 14]. The striking number of road traffic injuries and substance use could be due to the increased availability of low-cost motorization (motorcycles), poor road infrastructure, poor enforcement of traffic laws, low rates of education, high rate of unemployment, and poor socioeconomic status in combination with relatively cheap alcohol and drugs and poor law enforcement of regulations regarding drinking and driving [12, 25–27]. This is clearly an issue that deserves additional research, and these findings begin to provide the opportunity for stratification of behavior change campaigns and public health efforts.

In this study, the results of the substances abuse screening show that 57% of the patients denied the use of alcohol and 88% denied the use of illicit drug use before the injury while the objective testing showed that they were positive. Furthermore, the presumption of patient substance abuse use by their relatives was only 12% positive for alcohol and 31% positive for illicit drugs. The nurses and doctors’ patient presumption of substances abuse use was better for alcohol than for illicit drug use. This highlights the importance of analytic testing to define this issue. Although many studies worldwide have used patient’s verbal report or a questionnaire to screen for alcohol and illicit drug use in injured patients, our study and other studies, mostly conducted in HIC, have demonstrated that analytical testing is more accurate, gives the proof of substances abuse consumption, gives information when patients are unable to, and avoids under estimation of drug and alcohol use [7–9]. One of the biggest limitations of analytic testing in our setting is the high cost of alcohol and drug testing, and this is true in most LMICs [28].

At 24-h and 30-day followup we found that injured patients who tested positive for substance abuse were more likely to require major surgery than those who tested negative. The outcomes and relative risk findings above suggest that substance abuse contributes to more severe injuries leading to surgery, and that these trauma patients had high rates of prolonged return to the normal activities, and of death. Studies conducted in sub-Saharan Africa and HICs have shown similar outcomes [29, 30]. Regulations and education on alcohol and illicit drug use, and their acute and chronic effects should be implemented or reinforced on this matter, especially in Sub-Saharan Africa.

Limitations of this study include that it was conducted at ED-MNH, a tertiary care facility and national hospital. Therefore, the results might not be generalizable to other facilities in Tanzania. We tested illicit drugs using a multi drug panel test which could only give the results of five drugs. We may have missed additional illicit drugs that were not included in our drug screen. Finally, we did not measure injury severity directly, but instead used the need for surgical intervention, return to baseline, and death as proxy measures for injury severity.