14th October 2016, Volume 129 Number 1443

Judith Riley, Anna Hunt, Alice McDouall, Steve Waqanivavalagi, Irene Braithwaite, Mark Weatherall, Thorsten Stanley, Richard Beasley, Edwin A Mitchell, Stuart R Dalziel

Paracetamol (acetaminophen) use may be a risk factor both for the development of asthma and an increase in the severity of established asthma.1–8 Epidemiological associations between asthma and paracetamol exposure have been described in the intrauterine environment,9–14 infancy,3 later childhood4 and adult life.1,2,6 These associations may be confounded by indications such as respiratory tract infections, which are associated with an increased risk of asthma7,15 and a common reason for parents/guardians to use paracetamol in children.7,15 Paracetamol reduces circulating and airway glutathione levels, thereby potentiating increased oxidant-induced inflammation, either directly or by enhancing TH2 cell polarisation,16–20 hence leading to asthma.

Randomised controlled trials (RCTs) to investigate the association between paracetamol use and asthma are required in order to prove or disprove causality. There is one published RCT21 and one completed RCT published since the completion of this pilot study,22 comparing the effect of paracetamol versus ibuprofen use for fever and asthma outcomes in children with asthma. The former found that children with asthma had a decreased risk of out-patient asthma treatment when given ibuprofen compared to paracetamol, over a four-week period.21 In contrast, the latter study, a 48-week trial in which asthmatic children, aged from one to five years, were randomised to receive either paracetamol or ibuprofen administered per parental/guardian decision, for fever and analgesia, found no difference in asthma exacerbation rates, asthma control days or albuterol use between the paracetamol and ibuprofen groups.22 There are no RCTs assessing long-term risk of asthma in children who are naïve to paracetamol or ibuprofen in early infancy.

In order to complete a RCT assessing the long-term risk of asthma in children who are naïve to paracetamol in early infancy, a number of key feasibility questions need to be answered; firstly, the suitability and acceptability of possible comparators and secondly, if recruitment into a RCT is achievable. Previously, we approached parents/guardians of infants admitted into hospital with bronchiolitis to determine the acceptability of placebo, ibuprofen or ‘restricted’ paracetamol (in accordance with World Health Organization recommendations23) as comparators. This feasibility study established the non-acceptability of placebo and a clear preference for ibuprofen to be the comparator in future RCTs.24

Consequently we plan to undertake a RCT of paracetamol versus ibuprofen to be used (as required) exclusively from birth for fever and/or analgesia in order to determine if paracetamol use is associated with increased risk of asthma and atopic outcomes in childhood. In order to demonstrate a 25% reduction in risk of wheezing at age three years in those exposed to ibuprofen, 1,806 infants would need to be enrolled. The aim of this pilot study is to identify the most suitable recruitment domain for the proposed RCT from among antenatal classes, postnatal hospital wards or primary health care providers of the ‘six-week well-child visit’.

Methods

This pilot study was conducted in two New Zealand urban areas: Wellington and Auckland. Eligible participants were parents/guardians of yet-to-be-born or newborn infants, who attended antenatal classes, or were parents/guardians on a postnatal ward or parents/guardians of infants who attended a six-week well-child visit during the period 10 November 2014 to 28 February 2015 inclusive. Ethical approval was obtained from the New Zealand Southern Health and Disability Ethics Committee (HDEC 14/STH/83).

Following written informed consent, parents/guardians completed a two-part questionnaire: Part one collected demographic information of one parent and the infant; including family history of asthma, eczema and atopy. Part two investigated the likelihood of parents/guardians enrolling their infant into a proposed RCT (See Online Supplement).

Procedures

Antenatal domain: Study information was sent electronically to identified antenatal class coordinators in each centre where at least one class was scheduled to occur during the study period. In Wellington, permission was sought for study investigators to attend classes to promote the study and to recruit participants. Study investigators attended eight classes and spoke briefly to the whole class, answered any questions and then approached potential participants individually during break-time or after the class. Those who expressed interest, accepted a participant information sheet (PIS) and provided their contact details were followed up within three weeks. In Auckland, printed PISs and an introduction letter were provided to class coordinators who then handed these out to potential parents/guardians in 17 classes, mainly during discussions of postnatal infant care. Potential parents/guardians were invited to contact study investigators by phone or email for further information regarding participation.

Postnatal domain: Study investigators approached in-patient postnatal families in Wellington Regional Hospital (Wellington) and Middlemore Hospital (Auckland) during the hours of 9am to 4pm Monday to Friday over seven and eight weeks respectively. In Auckland, recruitment also occurred over two weekends. Potential parents/guardians were individually approached and offered study information; those deemed unsuitable by clinical staff were not. Numbers deemed unsuitable or who declined either the initial offer of information, or to participate, were recorded.

Six-week visit domain: Two Wellington-based primary health care providers gave out a letter containing study information to families who had a six-week well-child visit scheduled during the study period. Potential parents/guardians were invited to contact study investigators by phone or email for further information regarding participation.

Sample size and study power

As this was a pilot study to inform recruitment strategies for the proposed RCT, a formal sample size and power calculation was not undertaken prior to the study. We attempted to approach at least 100 possible parents/guardians in each domain as this was considered to give a sufficient comparison. We aimed to recruit 50 people from each of the three domains in both centres, giving a total of 300 completed questionnaires.

Statistical analysis

Primary outcome was the proportion of infants where parents/guardians indicated they would be ‘very likely’ or ‘likely’ to enroll their infant in the proposed RCT from each of the three domains studied. 95% confidence intervals were calculated using McCallum Layton Confidence Interval Calculator for Proportions.25 Secondary outcomes were the proportion of these infants, where parents/guardians indicated they would likely enroll the infant into the proposed RCT: i) whose mother has current asthma; and ii) with any first degree family member (mother, father or sibling) with current asthma. Parental/guardian concerns about convenience, study length and their child’s health were estimated from the answers given in the questionnaire.

Post hoc analysis was undertaken to determine the number of infant births required, and likely feasibility, to recruit the appropriate sample size (n=1,806) for the proposed RCT from the postnatal wards, over a two and three year recruitment window, for the following three potential recruitment scenarios: ‘Best’, recruiting all who indicated they were ‘very likely’ and ‘likely’ to participate in the proposed RCT; ‘Intermediate’, recruiting all who indicated they were ‘very likely’ and 50% who indicated they were ‘likely’ to participate in the proposed RCT; and ‘Worst’, only recruiting those who indicated they were ‘very likely’ to participate in the proposed RCT. The proposed RCT was determined feasible if the number of infant births required per year was less than the total births reported for Wellington, Middlemore and Auckland City Hospitals for 2013 (the anticipated sites for the proposed RCT). Enhanced recruitment for each scenario was further explored for the following strategies; 1) 25% of those who indicated they were ‘neutral’ participating in the proposed RCT, 2) recruitment occurring in the weekends and 3) recruitment occurring in the Satellite Birthing Units associated with the three hospitals.

Results

The flow of parents/guardians through the study is shown in Figure 1. Overall, 1,557 possible parents/guardians were identified over the study duration. 584 parents/guardians were approached via intermediaries (coordinators of antenatal classes and of six-week checks) to complete the study questionnaire. 456 parents/guardians were approached in person by the researchers. Questionnaires were only completed by parents/guardians who had been approached face-to-face by researchers. In the antenatal domain, of the eligible 586 parents/guardians, 112 were approached face-to-face, of whom 19 (17%) completed the study questionnaire. In the postnatal wards, of the 861 parents/guardians, 344 were approached face-to-face, of whom 196 (57%) completed the study questionnaire. None of the parents/guardians (0/110) who received a letter at the time of their infants’ six-week well-child check responded and none were seen face-to-face by the research team.

Figure 1: 

c 

Parent/guardian characteristics are shown in Table 1. Of the 215 parents/guardians who completed the questionnaire, 113 (53%) were female, with the cohort having a mean age of 32 years (SD six years) and having a median of 0 other children (range 0–8). European parents/guardians were more common in Wellington, while Pacific Island peoples were more common in Auckland. A history of personal/partner or sibling atopic disease was more common in parents/guardians recruited from Wellington.

Table 1:Characteristics of study participants who completed the questionnaire.

 

Wellington antenatal

n=19

Wellington postnatal

n=102

Auckland postnatal n=94

Parent mean age (SD), years

33±3

33±6

30±7

Median number of siblings of infant (range)

0 (0–1)

0 (0–8)

1(0–6)

Parent gender female

13 (68)

66 (65)

34 (36)

Parent ethnicity

European

16 (84)

73 (72)

21 (22)

Māori

2 (12)

8 (8)

11 (12)

Pacific

1 (5)

3 (3)

35 (37)

Asian

0 (0)

15 (15)

22 (23)

Other

0 (0)

3 (3)

5 (5)

History of asthma

Mother of infant

3 (16)

25 (25)

4 (4)

Father of infant

8 (42)

19 (19)

6 (6)

Any sibling of infant

0 (0)

10 (10)

4 (4)

History of eczema

Mother of infant

6 (32)

34 (33)

6 (6)

Father of infant

5 (26)

15 (15)

2 (2)

Any sibling of infant

0 (0)

2 (2)

4 (4)

History of hayfever

Mother of infant

5 (26)

33 (32)

6 (6)

Father of infant

8 (42)

37 (36)

5 (5)

Any sibling of infant

0 (0)

4 (4)

3 (3)

†Data are n (%) unless indicated.
‡’Parent’ refers to the parent/guardian who answered the questionnaire. 

Given the relative success of enrolment into the study by face-to-face recruitment with researchers while on the postnatal wards, we only report recruitment into the proposed RCT in this domain. Participation in a proposed RCT of three years duration was rated ‘very likely’, ‘likely’ and ‘neutral’ by 15 (8%, CI 4–12%), 65 (33%, CI 26–40%) and 64 (33%, CI 25–39%) of postnatal parents/guardians respectively. Participation in a proposed RCT of six years duration was rated ‘very likely’, ‘likely’ and ‘neutral’ by 5 (3%, CI 1–5%), 37 (19%, CI 14–25%) and 59 (30%, CI 24–36%) of postnatal parents/guardians respectively.

The proposed three-year RCT is deemed feasible for ‘Best’ and ‘Intermediate’ recruitment scenarios over a two- or three-year recruitment period from the postnatal wards of the three proposed recruitment domains (Table 2). Furthermore, the proposed three-year RCT is deemed feasible for ‘Worst’ recruitment scenario over a three-year recruitment period from the postnatal wards of the three proposed recruitment sites with enhanced recruitment strategies.

Table 2: Total number of live births required in all participating sites according to possible recruitment strategies and likelihood of enrolment into the proposed three-year RCT.

Recruitment strategy

Best recruitment

Intermediate recruitment

Worst recruitment§

Base case

Number of births required in participating hospitals

19,437

32,736

103,664

 -Annual number of births in participating hospitals if two years of recruitment

 9,719

16,368

 51,832

 -Annual number of births in participating hospitals if three years of recruitment

 6,479

10,912

 34,555

¶Enhanced recruitment - 25% of neutrals enroll

Number of births required in participating hospitals

16,198

24,488

50,160

 -Annual number of births in participating hospitals if two years of recruitment

 8,099

12,244

25,080

 -Annual number of births in participating hospitals if three years of recruitment

 5,399

 8,163

16,720

¶Enhanced recruitment - recruitment in weekends* 

Number of births required in participating hospitals

14,473

24,375

77,187

 -Annual number of births in participating hospitals if two years of recruitment

 7,236

12,187

38,594

 -Annual number of births in participating hospitals if three years of recruitment

 4,824

 8,125

25,729

¶Enhanced recruitment - recruitment from satellite hospitals*

Number of births required in participating hospitals

17,322

29,174

92,385

 -Annual number of births in participating hospitals if two years of recruitment

 8,661

14,587

46,192

 -Annual number of births in participating hospitals if three years of recruitment

 5,774

 9,725

30,795

¶Enhanced recruitment - all three strategies

Number of births required in participating hospitals

11,055

16,714

34,236

 -Annual number of births in participating hospitals if two years of recruitment

5,528

8,357

17,118

 -Annual number of births in participating hospitals if three years of recruitment

3,685

5,571

11,412

In 2013 there were 16,555 births in Wellington, Middlemore and Auckland City Hospitals (Data from Capital Coast, Counties Manukau and Auckland District Health Boards annual reports). The proposed paracetamol-ibuprofen randomised controlled trial is deemed feasible if the required number of births per year for the various recruitment scenarios is less than, or equal to, 16,555 (indicated in black). The proposed paracetamol-ibuprofen randomised controlled trial is deemed not feasible if the required number of births per year for the various recruitment scenarios is greater than 16,555 (indicated in bold black italic).

†Best recruitment: where all the “very likely” responders and all the “likely” responders enrol their infants.
‡Intermediate recruitment: where all the “very likely” responders and 50% of the “likely” responders enrol their infants.
§Worst recruitment: where only the “very likely” responders enrol their infants.
¶ Recruitment of additional participants occurs at same rate as base rate. 

The proposed six-year RCT is deemed feasible only for the ‘Best’ recruitment scenario over a three-year period from the postnatal wards and may become feasible over two years with addition of enhanced recruitment strategies (Table 3). The proposed six-year RCT is deemed infeasible with the worst recruitment scenario regardless of any enhanced recruitment strategies.

Table 3: Total number of live births required in all participating sites according to possible recruitment strategies and likelihood of enrolment into the proposed six-year RCT.

Recruitment strategy

Best recruitment

Intermediate recruitment

Worst recruitment§

Base case

Number of births required in participating hospitals

37,023

66,169

310,993

 -Annual number of births in participating hospitals if two years of recruitment

 18,512

33,084

155,497

 -Annual number of births in participating hospitals if three years of recruitment

 12,341

22,056

 103,664

Enhanced recruitment - 25% of neutrals enroll 

Number of births required in participating hospitals

27,400

40,653

78,732

 -Annual number of births in participating hospitals if two years of recruitment

 13,700

20,326

39,366

 -Annual number of births in participating hospitals if three years of recruitment

9,133

13,551

26,244

Enhanced recruitment - recruitment in weekends*

Number of births required in participating hospitals

27,567

49,269

231,562

 -Annual number of births in participating hospitals if two years of recruitment

 13,783

24,634

115,781

 -Annual number of births in participating hospitals if three years of recruitment

 9,189

 16,423

77,187

Enhanced recruitment - recruitment from satellite hospitals*

Number of births required in participating hospitals

32,995

58,969

277,155

 -Annual number of births in participating hospitals if two years of recruitment

16,497

29,485

138,577

 -Annual number of births in participating hospitals if three years of recruitment

 10,998

 19,656

92,385

Enhanced recruitment - all three strategies

Number of births required in participating hospitals

18,702

27,747

53,738

 -Annual number of births in participating hospitals if two years of recruitment

9,351

13,874

26,869

 -Annual number of births in participating hospitals if three years of recruitment

6,234

9,249

17,913

In 2013 there were 16,555 births in Wellington, Middlemore and Auckland City Hospitals (Data from Capital Coast, Counties Manukau and Auckland District Health Boards annual reports). The proposed paracetamol-ibuprofen randomised controlled trial is deemed feasible if the required number of births per year for the various recruitment scenarios is less than, or equal to, 16,555 (indicated in black). The proposed paracetamol-ibuprofen randomised controlled trial is deemed not feasible if the required number of births per year for the various recruitment scenarios is greater than 16,555 (indicated in bold black italic).

†Best recruitment: where all the “very likely” responders and all the “likely” responders enrol their infants.
‡Intermediate recruitment: where all the “very likely” responders and 50% of the “likely” responders enrol their infants.
§Worst recruitment: where only the “very likely” responders enrol their infants.
¶ Recruitment of additional participants occurs at same rate as base rate. 

Potential barriers to participation

Parental/guardian concerns regarding convenience, study length and their child’s health on possible participation are shown in Table 3. Overall, the 52 parents/guardians who rated possible participation as ‘unlikely’ or ‘very unlikely’ had greater levels of being ‘concerned’ or ‘very concerned’ in terms of convenience study length, and the effect on their child’s health of participation in the study compared with the other parents/guardians (p<0.01 for all three comparisons). Of the 80 parents/guardians who rated possible participation as ‘likely’ or ‘very likely’, 26 (33%) were ‘concerned’ or ‘very concerned’ about the effect on their child’s health of participation in the proposed RCT. Narrative responses identified 17 (9%) parents/guardians wanting the choice of medication, 10 (5%) unwilling to use ibuprofen for a child under three years of age, seven (4%) likely to travel overseas within three years and six (4%) who stated a need for more information about both medications.

Table 4: Potential barriers to participation in a randomised controlled trial of three years duration.

 

Participation N (%) ‘Likely’ and ‘Very likely’ (n=80)

Participation N (%) ‘Neutral’ (n=64)

Participation N (%)‘Unlikely’ and ‘Very unlikely’ (n=52)

Convenience

‘Very inconvenient’/‘Inconvenient’

8 (10)

13 (20)

26 (50)

‘Neutral’

26 (33)

35 (55)

17 (33)

‘No trouble’

46 (58)

16 (25)

9 (17)

Study length

‘Very concerned’/‘Concerned’

11 (14)

27 (42)

28 (54)

‘Neutral’

28 (35)

20 (31)

11 (21)

‘No trouble’

41 (52)

17 (27)

13 (25)

Your child’s health

‘Very concerned’/‘Concerned’

26 (33)

32 (50)

40 (77)

‘Neutral’

27 (34)

25 (39)

8 (15)

‘Not concerned’

27 (34)

7 (11)

4 (8)

Secondary outcomes

Twenty-four (12%) postnatal parents/guardians had at least one first-degree relative with current asthma. Of these families, 17 (71%) and 14 (58%) responded ‘likely’ or ‘very likely’ to participate in the proposed RCT of three years and six years duration respectively. Current maternal asthma was reported in 14 (7%) parents/guardians. Of these, 11 (79%) and eight (57%) responded ‘likely’ or ‘very likely’ to participate in the proposed RCT of three years and six years duration respectively.

Discussion

This pilot study showed that the most successful recruitment domain for the proposed paracetamol-ibuprofen RCT is likely to be the postnatal wards. As the study progressed it became obvious that this recruitment strategy was superior to recruitment from antenatal classes or six-week checks, answering the primary objective of the study. Eighty (23%) of the 344 parents/guardians who were approached face-to-face in the postnatal wards indicated that they were ‘very likely’ or ‘likely’ to enroll their newborn infant into the proposed RCT of three years duration.

The comparatively high number of questionnaires answered in the postnatal wards is most likely due to accessibility of investigators, face-to-face recruiting and the ability to allow parents/guardians to answer questions and make decisions regarding participation over time. In contrast, antenatal recruiting was often limited to a single-class period for multiple parents-to-be, and the six-week well-child visit was dependent on new parents/guardians acting on written information given to them. For the proposed RCT, concentrating recruitment resources at a few postnatal locations appears to be the most efficient recruitment strategy. The postnatal domain also allows access to a population sample with broader demographics compared to antenatal classes, which tend to attract first-time parents and those in higher socio-economic groups.26,27

Previously researchers in New Zealand have enrolled infants from both the antenatal and postnatal environments in large numbers for either long-term observational studies28 or short-term interventional studies in selected at-risk or pathological populations.29 To our knowledge, recruitment of large numbers of newborn infants from the general population into a long-term interventional study in New Zealand has not occurred. Given that the arrival of a newborn infant is a time of increased stress, it is very possible that recruitment into a long-term interventional study would not be successful. Thus this current study provides important information regarding the feasibility of undertaking the proposed RCT. Furthermore, the findings are generalisable to others who may be planning large long-term interventional studies in New Zealand infants from birth.

Accurate prediction of the real enrolment rate into RCTs is problematic. When assessing the feasibility of the proposed RCT we calculated recruitment from the 80 of the 861 potential parents/guardians identified on the postnatal wards, who indicated that they would ‘very likely’ or ‘likely’ enroll their newborn infants into the proposed RCT. These results are not generalisable to the antenatal or six-week check groups and given the low response rates from these two groups, they were excluded from possible recruitment calculations. Postnatal recruitment rates could be enhanced by strategies to encourage the ‘neutral’ group (33% of those who completed the questionnaire) to consider enrolling their infants, recruiting from satellite postnatal locations, recruiting outside of regular working hours and providing study information to all parents/guardians in the postnatal ward.

Recruitment of infants with a higher risk of developing asthma, such as those with a first degree relative with asthma, would increase the power of the proposed RCT. In our current study the potential recruitment rate in this sub-population (12% of population) was higher than the remainder of the sample. However, the percentage of newborn infants meeting this category would make limiting recruitment to this cohort impractical. By enrolling infants into the proposed RCT from a general population, the subsequent results would be broadly generalisable, but reassuringly still provide important information on the sub-population of those with a first-degree relative with asthma.

There are a number of limitations to this study. Firstly, all antenatal classes attended by study investigators were aimed at first-time parents/guardians. Study information was not provided to parents/guardians expecting a second or subsequent child and thus we were unable to explore antenatal recruitment in this population. Secondly, the study sample was a convenience sample and thus at risk of selection bias. However, as recruitment into the proposed RCT is likely to occur predominantly in the same working hours this is unlikely to have a significant effect. Thirdly, the current study is a pilot study and recruitment rates into the proposed RCT may not reflect parents/guardians responses to a questionnaire.

Conclusion

Recruitment into a large (n=1,806) long-term RCT of paracetamol versus ibuprofen is likely to be successful from postnatal wards but not from antenatal clinics and six-week well-child visits. By recruiting from postnatal wards in three large hospitals, the proposed RCT is likely to be feasible at high and intermediate recruitment rates, and at low rates with enhancement of recruitment strategies.

Summary

This pilot study assessed the likelihood of recruiting infants into a study that would randomly allocate infants to use only paracetamol or ibuprofen for fevers and pain from birth until the age of one year, and to then compare the rates of asthma between the two groups when the children turned six years old.

Abstract

Aim

To undertake a randomised controlled trial (RCT) of paracetamol versus ibuprofen use during infancy to determine if paracetamol is associated with an increased risk of developing asthma, the preferred method of recruitment needs to be determined. We assessed three different recruitment domains to determine the likely enrolment rates of newborn infants into a three-year or six-year RCT of paracetamol versus ibuprofen and the development of asthma symptoms. The proposed RCT would require 1,806 participants.

Method

A questionnaire was administered to a convenience sample of Auckland and Wellington based parents/guardians within three different recruitment domains: antenatal classes, postnatal wards and six-week well-child visits at primary healthcare centres.

Results

Over a twelve-week period 19/586 (3.2%), 196/861 (22.8%), and 0/110 (0%) questionnaires were completed by parents/guardians of newborn infants in antenatal, postnatal and primary healthcare domains. In the postnatal recruitment domain, the likelihood of newborn infants being enrolled in the proposed RCT was rated ‘very likely’, ‘likely’ and ‘neutral’ by 15 (8%, CI 4–12%), 65 (33%, CI 26–40%) and 64 (33%, CI 25–39%) of respondents for a RCT of three years duration; and by 5 (3%, CI 1–5%), 37 (19%, CI 14–25%) and 59 (30%, CI 24–36%) of respondents respectively for a RCT of six years duration.

Conclusion

Postnatal wards are expected to be the most successful recruitment domain for the proposed RCT, likely a reflection of the face-to-face direct recruitment by researchers. It appears feasible to recruit into the proposed RCT using three large New Zealand tertiary hospitals.

Author Information

Judith Riley, Research Nurse, Medical Research Institute of New Zealand, Wellington; Anna Hunt, Research Nurse, Medical Research Institute of New Zealand, Wellington; Alice McDouall, Summer Student, Medical Research Institute of New Zealand, Wellington; Steve Waqanivavalagi, Summer Student, The University of Auckland, Auckland; Irene Braithwaite, Research Fellow, Medical Research Institute of New Zealand, Wellington; Mark Weatherall, Consultant Geriatrician, Capital and Coast District Health Board, Professor of Medicine, University of Otago, Wellington; Thorsten Stanley, Consultant Paediatrician, Capital and Coast District Health Board, Senior Lecturer, University of Otago, Wellington; Richard Beasley, Director, Medical Research Institute of New Zealand, Respiratory Physician, Capital and Coast District Health Board, Wellington; Edwin A Mitchell, Professor, Paediatrics (Child and Youth Health), School of Medicine, The University of Auckland, Auckland; Stuart R Dalziel, Specialist, Liggins Institute, The University of Auckland, Paediatric Emergency Medicine Specialist, Auckland District Health Board, Auckland.

Acknowledgements

We would like to thank the parents/guardians who participated in this pilot study, the staff at the maternity units at Capital and Coast District Health Board and Auckland District Health Board, the Lead Maternity Carers who invited us into their antenatal classes and the general practices that worked with us during this pilot study.

Correspondence

Dr Irene Braithwaite, Research Fellow, Medical Research Institute of New Zealand, Wellington.

Correspondence Email

irene.braithwaite@mrinz.ac.nz

Competing Interests

Ms McDouall reports grants from Capital Coast District Health Board during the conduct of the study.

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