Study design and population
This study was a cross-sectional survey including patients 18–65 years old identified via specialist centres in Sweden. Two groups of patients with specific IgE-confirmed grass pollen allergy were identified; one had received at least 12 months of SLIT treatment against grass pollen allergy, n = 307, whereas the other cohort of individuals, the reference population, were waiting to start up SCIT against grass pollen and/or birch pollen allergy, n = 241. During the waiting period the latter group had received standard of care pharmacological treatment. The definition of “standard of care” was, per protocol, left to the judgement of the investigators, which were all experienced physicians (ENTs or Pulmonologists or Allergy specialists) working at specialized allergy or ENT-centers in Sweden that perform allergen immunotherapy on a routine basis.
The optimal reference group for the SLIT cohort would have been patients waiting for SLIT, but since SLIT in Sweden usually starts more or less upon referral, there is practically no waiting list for this therapy. Thus, patients waiting for SCIT were used for the comparison. Only Grazax®, also known as Grastek®, 75,000 SQ-T tablets (ALK-Abelló A/S, Denmark) is available for grass pollen SLIT in Sweden.
A questionnaire was mailed, after the birch and grass seasons, to the two groups of AR patients with a valid postal address in Sweden. Distribution was done by regular mail in September 2017 (a postal reminder was sent out approximately 2 weeks after the first letter) to capture the seasonal allergies season from March to August the same year. The questionnaire included questions on age, gender, employment status, sick leave, health care resource utilization during the past year and quality of life as measured by EQ-5D-3L [6].
Inclusion criteria were age 18–65 years, a valid address in Sweden and prick test or specific IgE-confirmed grass pollen allergy. The only exclusion criterion was lack of ability to read and write Swedish.
The primary objective of this cross-sectional survey was to analyse the health-economic consequences in terms of direct and indirect costs and quality of life in the treatment of grass allergy with SLIT for grass pollen allergy in Sweden vs a reference group with standard of care, waiting for SCIT.
Health-economic analyses
Direct costs were calculated for pharmaceuticals and for health care contacts related to allergic nasal/eye problems (physician visits, nurse visits and telephone consultations). Unit costs for health care contacts were collected from the price list for the Southern Health Care Region [7]. Unit costs for pharmaceuticals were collected from “FASS” (Pharmaceutical Specialities in Sweden, the Swedish Drug Information site) [8].
When calculating the number of days for questions answered with intervals, the middle value for the interval was used. In cases where a response gives more than a certain value, the minimum exceeding the value was used to provide a conservative estimate. Costs were not calculated for SCIT treatment in accordance with the definition of the included population.
Indirect costs included costs for productivity loss due to both sick-leave, i.e. absenteeism, and impaired working capacity, i.e. presenteeism. Productivity losses were calculated according to the human capital approach [9] using the average yearly income from work and adjusting for payroll taxes by multiplying by 1.43 (the mean employment payroll taxes for the Swedish population is 43%) [10,11,12]. The maximum occupation level was assumed to be 100%. For respondents reporting several part-time occupations the sum of the part-time occupations was used up to 100%. For respondents reporting a part-time occupation without specifying the extent, a 50% occupation level was assumed.
The productivity loss due to absenteeism was calculated by multiplying days of reported sick leave by sex and age-adjusted mean wage including payroll taxes. Productivity loss due to presenteeism was likewise calculated but multiplied with the estimate where the respondent indicated to what extent productivity was reduced while working with allergic nasal eye problems. When calculating costs related to presenteeism and absenteeism, answers indicating a longer season than 4 months are set to only include the four months relevant to the pollen season as not to overestimate the indirect costs.
The presented mean costs were calculated on a sample limited to the working population, i.e. approximately 80% of the total study population. This approach was used to avoid skewing the mean total and indirect costs (Additional file 1: Table S1).
Swedish costs were converted to Euros, €, using the average exchange rate 2017.
Statistical analyses
Descriptive statistical analyses were conducted for all questions in the survey and for direct, indirect and total costs. Differences between groups were assessed with t-tests for continuous variables and Chi-squared tests were used for categorical variables. All tests were performed at the 0.05 level of significance and were two-sided.
Statistical analyses were performed using STATA, version 14 for Windows (StataCorp, Stata Statistical Software: Release 14. 2015, StataCorp LP: College Station, TX, USA).
