How is enrolment with a general practice associated with subsequent use of the emergency department in Aotearoa New Zealand? A cohort study

Introduction

In many countries, primary health care (PHC) is the most common way to access a range of health care services. PHC, as well as providing health services in a community setting, can prevent or reduce the need for secondary and tertiary health care through health promotion and early medical intervention, and can facilitate access to other health and social care.¹ Reducing the need for secondary and tertiary health care assists in lowering overall health system costs.²

In Aotearoa New Zealand (NZ), people are able to access PHC at a general practice. The extra step of enrolling gives people added benefits, which may include reduced user charges and access to specific health programmes, such as screening or counselling. However, enrolling may not always be possible at a desired general practice if the practice has closed its books to enrolment.³ In 2022, 33% of general practices in NZ had closed their books.⁴ There are also rural–urban disparities in general practice coverage and in socioeconomically deprived urban areas making access to enrolment difficult. In addition, certain classes of visitors to NZ and new migrants may not be eligible to enrol, at least initially.⁵ General practices benefit from enrolling patients as they gain funding for each patient enrolled, through a capitation formula.⁶

In 2023, around 5% of the population was not enrolled in a general practice and this has been found to differ by age, ethnicity and deprivation, with Māori and Pacific peoples (when compared explicitly to non-Māori/non-Pacific peoples), young people and those who live in more socioeconomically deprived areas having lower enrolment rates.⁷

The aim of this study was to better understand the way in which people who were not enrolled access care. On the one hand, those not enrolled may bypass general practice and access care through an emergency department (ED). On the other, those not enrolled may delay seeking care or face barriers to seeking care in general practice and end up in an ED when they become unwell.

For this study, we took a cohort of respondents from the New Zealand Health Surveys (NZHS) and ascertained who were enrolled in a general practice and who were not enrolled. From the survey data, we compared these groups by their use of health care in general practice and substitutes. Finally, we looked at their use of EDs in the years following the survey they participated in.

Methods

The data for this study were accessed via the Datalab at Statistics New Zealand.⁸ For a fuller account see the supplementary material accompanying this paper.

Five data sets were accessed and combined via the encrypted National Health Index. These were six NZHS surveys with data collected between 2013/14 and 2018/19 which provided self-reported information about the demographics, health care and health status of respondents. The Primary Health Organisation Enrolment data set and the National Enrolment Service data set gave information about enrolment status in general practice. The National Non-Admitted Patient Collection dataset gave information about presentations in EDs at public hospitals. The Mortality data set gave information about deaths.

Results

In the Datalab, the combined number of respondents across the six NZHS surveys was 72,243. Some respondents died before follow-up started (225, 0.3% of observations deleted). There were also some respondents in more than one survey for whom one random observation was chosen (516, 0.7%, observations deleted). This meant the analysis data set consisted of 71,502 respondents. See Supplementary Fig. S2 for a figurative description.

Discussion

Those not enrolled are more likely to be male, young and Asian compared to the enrolled. They are more likely to be living in the more socioeconomically deprived quintiles, to have better health and be less likely to have chronic diseases compared to those enrolled. Being younger, male and healthier suggests a perception of good health which explains why people choose not to enrol.

The young are also more likely to be transient, moving for education, work and new relationships which may hinder new enrolment or enrolment continuity. Those that are not enrolled are more likely to be young, for whom incomes tend to be lower, and live in more socioeconomically deprived quintiles, which suggests that affordability of accessing care may be an issue. While not-enrolled people consult GPs less frequently than the enrolled, they still experience unmet health care needs, particularly in terms of cost for both GP and after-hours consultations. Additionally, those not enrolled are more likely to opt for ED visits, where treatment is free, for conditions that could have been addressed in general practice.

While those not enrolled are more likely to be male, young, Asian, more socioeconomically deprived and in better health, they were not uniformly so. That there are respondents with chronic conditions eg diabetes and depression, who are not enrolled, indicates that they are a heterogeneous group with a range of needs.

Asian people in this cohort are the ethnic group least likely to be enrolled. This seems at odds with other research which found that Māori were the ethnic group least likely to be enrolled (compared to Pacific peoples and non-Māori/non-Pacific peoples).⁷ Starting in 2019, the MoH released a data series that allowed analysis of Asian people as their own separate ethnic group. The data from the June 2019 quarter gives the closest data available in time to the data reported here. It showed that enrolment rates per 100 population were 76% for Asian people compared to 82% for Māori.^11,12 This supports our finding that the Asian population in the survey data had lower enrolment rates.

One hypothesis could be that the not-enrolled group could be disproportionately capturing new migrants who may be ineligible to enrol.⁵ New migrants were removed from the data set and the hazard rate for the not-enrolled group in Model 3 changed by 1.5% suggesting that eligibility to enrol is not driving the difference between the enrolled and not-enrolled results.

Altogether, the statistics have shown that those who are not enrolled are clearly getting fewer health services and there is reason to believe they are getting fewer health services than they need. An analysis of a complete collection of deaths in NZ between 2008 and 2017 found that those who died from an amenable death were more likely to not be enrolled, after adjusting for age, sex, ethnicity and socio-economic deprivation.¹³

The strength of this analysis is that it is able to draw on a large pool of respondents with wide-ranging information on their health service use. However, the NZHS does not reach people in outlying islands, those in hospital level care and those without a place of residence. In the 2018 census, just over 3500 people were in the group labelled ‘people without shelter’.¹⁴ It is more likely that this group had greater unmet need for health care and lower access to enrolment than the general population. In addition, those refusing to participate in the NZHS may have different characteristics to those that do.

Around 8% of the respondents in the NZHS were not included in the Integrated Data Infrastructure (IDI) dataset because they could not be matched to a National Health Index (NHI) number. It is extremely unlikely that those in the sample frame would not have a NHI number (personal communication, MoH) so not being able to make a match suggests either errors in recorded personal information or non-matches in home address. A study found that transience (moving more than three times in 3 years) occurs in around 5.5% of the population and 4.3% were considered vulnerable transients (had at least one housing occurrence in a socioeconomically deprived area).¹⁵ It seems likely that the unmatched respondents were more likely to not be enrolled and more likely to be socioeconomically deprived than the not-enrolled group studied here.

A limitation of this analysis is not knowing the interview dates of participants in the NZHS. To address this, we opted to start our study period at the conclusion of each survey period. As part of a sensitivity analysis, we re-analysed Model 3 but set the start date of follow-up to match the beginning of the survey period. This adjustment resulted in a 5% alteration of the hazard ratios for enrolment status, with the change being in the conservative direction.

There are significant differences between the enrolled and not-enrolled groups and the health services they use. To achieve the goals of equity in health and access to care,¹⁶ it is important to ensure that all populations enjoy equal opportunities to access health services, in particular PHC services, regardless of their economic means or other socioeconomic circumstances.

Supplementary material

Supplementary material is available online.