Global patterns of mortality in international migrants: a systematic review and meta-analysis

Abstract

Background: 258 million people reside outside their country of birth; however, to date no global systematic reviews or meta-analyses of mortality data for these international migrants have been done. We aimed to review and synthesise available mortality data on international migrants.

Methods: In this systematic review and meta-analysis, we searched MEDLINE, Embase, the Cochrane Library, and Google Scholar databases for observational studies, systematic reviews, and randomised controlled trials published between Jan 1, 2001, and March 31, 2017, without language restrictions. We included studies reporting mortality outcomes for international migrants of any age residing outside their country of birth. Studies that recruited participants exclusively from intensive care or high dependency hospital units, with an existing health condition or status, or a particular health exposure were excluded. We also excluded studies limited to maternal or perinatal outcomes. We screened studies using systematic review software and extracted data from published reports. The main outcomes were all-cause and International Classification of Diseases, tenth revision (ICD-10) cause-specific standardised mortality ratios (SMRs) and absolute mortality rates. We calculated summary estimates using random-effects models. This study is registered with PROSPERO, number CRD42017073608.

Findings: Of the 12 480 articles identified by our search, 96 studies were eligible for inclusion. The studies were geographically diverse and included data from all global regions and for 92 countries. 5464 mortality estimates for more than 15·2 million migrants were included, of which 5327 (97%) were from high-income countries, 115 (2%) were from middle-income countries, and 22 (<1%) were from low-income countries. Few studies included mortality estimates for refugees (110 estimates), asylum seekers (144 estimates), or labour migrants (six estimates). The summary estimate of all-cause SMR for international migrants was lower than one when compared with the general population in destination countries (0·70 [95% CI 0·65-0·76]; I²=99·8%). All-cause SMR was lower in both male migrants (0·72 [0·63-0·81]; I²=99·8%) and female migrants (0·75 [0·67-0·84]; I²=99·8%) compared with the general population. A mortality advantage was evident for refugees (SMR 0·50 [0·46-0·54]; I²=89·8%), but not for asylum seekers (1·05 [0·89-1·24]; I²=54·4%), although limited data was available on these groups. SMRs for all causes of death were lower in migrants compared with the general populations in the destination country across all 13 ICD-10 categories analysed, with the exception of infectious diseases and external causes. Heterogeneity was high across the majority of analyses. Point estimates of all-cause age-standardised mortality in migrants ranged from 420 to 874 per 100 000 population.

Interpretation: Our study showed that international migrants have a mortality advantage compared with general populations, and that this advantage persisted across the majority of ICD-10 disease categories. The mortality advantage identified will be representative of international migrants in high-income countries who are studying, working, or have joined family members in these countries. However, our results might not reflect the health outcomes of more marginalised groups in low-income and middle-income countries because little data were available for these groups, highlighting an important gap in existing research. Our results present an opportunity to reframe the public discourse on international migration and health in high-income countries.

Funding: Wellcome Trust, National Institute for Health Research, Medical Research Council, Alliance for Health Policy and Systems Research, Department for International Development, Fogarty International Center, Grand Challenges Canada, International Development Research Centre Canada, Inter-American Institute for Global Change Research, National Cancer Institute, National Heart, Lung and Blood Institute, National Institute of Mental Health, Swiss National Science Foundation, World Diabetes Foundation, UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, and European Society for Clinical Microbiology and Infectious Diseases (ESCMID) Study Group Research Funding for the ESCMID Study Group for Infections in Travellers and Migrants.

Figure 1

Study selection

Figure 2

Forest plots of SMRs for all-cause mortality Studies are presented as region of origin, country of study (study [year]). Data are presented for male individuals (A) and female individuals (B). 13 studies reported all-cause mortality estimates, of which 53 estimates were available for men, and 50 were available for women. SMR=standardised mortality ratio.

Figure 2

Forest plots of SMRs for all-cause mortality Studies are presented as region of origin, country of study (study [year]). Data are presented for male individuals (A) and female individuals (B). 13 studies reported all-cause mortality estimates, of which 53 estimates were available for men, and 50 were available for women. SMR=standardised mortality ratio.

Figure 3

Forest plots of SMRs for all-cause mortality by migrant group Studies are presented as region of origin, country of study (study [year]). 16 studies reported all-cause mortality estimates by migrant group, which included 119 mortality estimates. SMR=standardised mortality ratio.

Figure 4

Meta-analysis estimates of SMRs for international migrants by ICD-10 disease category SMR=standardised mortality ratio. ICD-10=International Classification of Diseases, tenth revision.

Figure 5

Subgroup analysis of international migrants by ICD-10 subgroup disease category for the six ICD-10 disease categories with the highest total number of SMR estimates Data are presented for neoplasms (A), the circulatory system (B), external causes (C), respiratory diseases (D), infection (E), and endocrine disorders (F). SMR=standardised mortality ratio. ICD-10=International Classification of Diseases, tenth revision.