The prevalence of chronic pain with an analysis of countries with a Human Development Index less than 0.9: a systematic review without meta-analysis

Background: To date, there are no systematic reviews of epidemiological studies of chronic pain in the developing world. Aim: To estimate the prevalence of chronic pain worldwide paying particular attention to data from countries with a Human Development Index (HDI) of less than 0.9. Methods: A literature search was conducted for cross-sectional surveys of chronic pain (>= 3 months) in the adult general population using Medline, Embase, CINAHL, SportDiscus, Sciencedirect, CAS ILLUMINA, Academic search complete, PsycINFO and AMED. Forty-eight studies were identified and 29 of these were excluded because they surveyed children, the elderly or were longitudinal studies. Results: Weighted mean +/- SD prevalence of chronic pain worldwide was 30.3% +/- 11.7% (19 studies, 65 surveys, 34 countries, 182,019 respondents). There was no correlation between HDI and prevalence. In countries with a HDI<0.9 prevalence was 33.9% +/- 14.5% and significantly higher than prevalence in countries with a HDI of >= 0.9 (29.9% +/- 12.7%), although removal of a large study that may have included a sample of individuals with comorbidities reduced the worldwide estimate to 28.0% +/- 11.8% (47 surveys, 33 countries, 139,770 participants). Interestingly, the estimate of countries with a HDI<0.9 to 24.8% +/- 8.9% (7 surveys, 7 countries, 6122 participants) became significantly lower than the estimate of countries with a HDI >= 0.9 which was 28.1% +/- 11.6% (40 surveys, 21 countries, 133,648 participants). Conclusion: The review provides further evidence that the prevalence of chronic pain in the general population is high. However, there was insufficient reliable data to estimate with any certainty the prevalence of chronic pain in countries with an HDI<0.9 with variability in estimates between surveys being of concern. Subtle differences in review and survey methodology appeared to impact markedly on estimates. There is a need for epidemiological studies that estimate the prevalence of chronic pain in developing countries to determine the scale of the problem.