About the study

Background

More than 40 million people are living with HIV worldwide. Antiretroviral therapy has transformed the prognosis: overall life expectancy for people living with HIV is now close to that of people without HIV, and those who reach good immune recovery early after starting treatment appear to have a life expectancy similar to the general population.

Yet a consistent picture has emerged from research over the past decade. People living with HIV have a higher risk of a wide range of other conditions. They are reported to more often develop inflammatory conditions, with a higher burden of diseases such as diabetes and atherosclerosis, which in turn raise the risk of hospital admission and death. Cardiovascular disease is now among the leading causes of illness and death in people receiving antiretroviral therapy, with an estimated more than twofold higher incidence than in people without HIV. The risk of several cancers is also raised, particularly infection-related cancers, where impaired immune control of oncogenic viruses is thought to be the main mechanism. Incidence has fallen since effective treatment became available, but it remains higher than in the population without HIV.

The causes are almost certainly multiple: chronic HIV-related inflammation, the legacy of immunodeficiency and organ injury from before treatment started, the effects of past and present medication, and the fact that the population living with HIV is ageing and therefore meeting age-related illness. How much each of these contributes is not known. Half of all people with HIV are still diagnosed late, with well-documented consequences for prognosis. And even among those who reach the treatment goal of an undetectable viral load, health-related quality of life has been shown to be poorer than in the population without HIV.

Most previous studies of these questions have not been able to separate the effect of HIV itself from the effect of everything else. Population-based cancer studies, for example, have often compared people with HIV to general population figures without adjusting for socioeconomic circumstances or country of birth on an individual level. And a majority of HIV cohorts studying comorbidity have consisted of 80–90 % white men, leaving women and migrant populations badly under-represented.

Why Sweden

Sweden is unusually well placed to answer these questions. The Swedish HIV quality register, InfCareHIV, includes more than 99 % of everyone diagnosed with HIV in the country. It is also heterogeneous in a way that few cohorts are: around 40 % of those in care are women, about two-thirds were born outside Sweden — in more than a hundred countries on every continent — and the cohort covers diverse routes of HIV acquisition and a wide range of socioeconomic backgrounds.

Because everyone resident in Sweden has a personal identity number, this cohort can be linked to national registers covering hospital care, cancer, prescribed medicines, causes of death, income, education and employment. That makes it possible to compare people living with HIV to the rest of the population while adjusting for the factors that would otherwise confound the comparison — and so to get closer to the effect of HIV infection itself.

Aim

The overall aim of COSMOHS is to analyse which factors contribute to morbidity, mortality and health-related quality of life among people living with HIV in Sweden, compared with the population living without HIV, and how these change over time. This will form a knowledge base for preventive initiatives and treatment guidelines.