The Swiss healthcare system is well known for the quality of its health care and population health [1,2], but also for its high cost, particularly out-of-pocket expenses [3,4]. The country ranks well on several population health outcomes [2], including premature mortality from conditions amenable to healthcare interventions (amenable mortality) which is among the lowest in the world. Switzerland's affluence, along with the design of its healthcare system, contribute to its spending among the highest shares of gross domestic product on healthcare compared to other nations of the Organization for Economic Cooperation and Development (OECD). Likewise, the nation's wealth and health system design contribute to Switzerland's out-of-pocket (OOP) spending (in the form of deductibles and cost sharing) which exceeds that of the United States (US) both as a percent of total healthcare expenditures, respectively 26% and 11%, and in absolute amounts under purchasing power parity, respectively 1,838 US dollars and 1,183 US dollars [5,6].

High OOP spending may create inequity in access to care between affluent and deprived individuals in the form of forgone healthcare [7]. We expect that forgone community-based ambulatory care (CBAC) which we define as the services provided by general practitioners (GP) and specialists working outside of hospitals, leads many individuals, particularly those with low income, to present to hospital emergency rooms and then be admitted for inpatient hospital stays once their chronic health conditions worsen and care can no longer be avoided. Switzerland provides an adequate laboratory to study these effects due to the design of its healthcare system.

Previous studies conducted in Switzerland have documented socioeconomic gradients in health status (e.g., ischemic heart disease mortality) and access to healthcare [8,9]. They have also noted the association between health literacy and barriers to healthy eating [10], and healthcare expenditures [9]. In addition, there are studies on variations in rates of potentially avoidable hospitalizations (PAH) among nursing home residents [11] and the general population [12,13]. Berlin et al. [12] also noted that physician density and rurality are relevant determinants of PAH. A recent report by Bayer-Oglesby et al. [14] documents a socioeconomic gradient in the risk of hospitalization due to chronic conditions, in particular for ambulatory care-sensitive conditions.

In this paper, we aim to assess equity of access to CBAC at the national and local levels and provide a comprehensive analysis of national data at the small area level on the association between socioeconomic conditions and PAH, a widely accepted indirect measure of access to CBAC [15], [16], [17], [18], [19], [20], [21], [22]. PAH, also referred to as hospitalizations for ambulatory care sensitive conditions are residence-based hospital discharges that could have been avoided with the provision of timely and effective CBAC, “by preventing the onset of an illness or condition […] or managing a chronic disease or condition” [23]. PAHs are associated with characteristics of the healthcare system and its organization, such as the density of CBAC providers, as well as patient-level or environmental-level factors such as income, education, deprivation, migration status or mental health comorbidities [12,18,20,21,24]. They provide an adequate tool to measure access to CBAC in our study for the following reasons. First, as is it well documented in the literature, PAHs reflect a range of barriers in access to CBAC including the effects of forgone healthcare due to high OOP payments. Second, the indicator is derived from hospital discharge data that are readily accessible and reliable for Switzerland in contrast to information on the use of CBAC services, which is typically sparse, difficult to access, and of poor quality, particularly within cantons at the small area level.

The Swiss population is covered by a mandatory, universal and comprehensive health insurance system that allows for extensive consumer choice of regulated insurance plans and healthcare providers [25]. Performance on equity in financing is weaker than in other high-income countries [3,4] because individuals’ health insurance premiums are not income-related, resulting in low-income households spending a disproportionate share of their disposable income on healthcare [1,2,26]. Mandatory health insurance premiums do not depend on ability to pay, except through government-funded premium subsidies aimed at low-income households. Another feature of the Swiss healthcare system is its highly decentralized institutional structure, with many key decisions, including the level of premium subsidies, under the responsibility of the 26 cantons (“states”), which results in virtually 26 different healthcare systems [27,28] with significant geographic disparities in access to healthcare among them.

The standard health insurance plan includes a yearly deductible of CHF 300 followed by a 10% coinsurance upon reaching the deductible with a yearly stop loss set at CHF 700 (i.e., individuals could spend a maximum of CHF 1000 in OOP). The plan also includes free choice of provider, which means that consumers may consult with any GP or specialist. In an effort to control the rising costs of health insurance, higher deductible levels can be selected (with a maximum of CHF 2500) in exchange for lower premium payments. Individuals can also lower their premiums if they opt for alternate plans that restrict choice of provider, for example by removing the ability to self-refer to specialists. All plans share the same comprehensive healthcare coverage. Registration with a physician is not mandatory but unregistered patients may face longer waiting times to get an appointment.