Rheumatic Fever Hospitalisation in the Toi Te Ora – Public Health Service Area ( and Lakes District Health Boards) Update Report 2014

Summary

Rheumatic fever is a serious illness and has a high rate, particularly among Maori and Pacific children and young adults1. It is one of the Governments 10 Better Public Services results and targets a reduction in the incidence of rheumatic fever by two thirds by June 20172. Both the Bay of Plenty District Health Board (DHB) and Lakes District Health Board (DHB) are regarded by the Ministry of Health as having high rates of rheumatic fever. This report summarises data on initial hospitalisations for rheumatic fever for Bay of Plenty and Lakes DHB residents for the 2009-2013 period.

The relatively small number of cases of rheumatic fever means that there are limits to our ability to accurately measure differences between areas with small populations. Confidence intervals are quite wide and show the limited precision of rheumatic fever rates calculated for small groups.

It is also difficult to make accurate statements about trends over time because of the small number of cases for a low prevalence condition like rheumatic fever. Some years there are higher numbers and year to year fluctuation can be expected. Different analysis methods yield varied results. For example, different patterns can be found depending on whether financial years or calendar years are chosen for analysis. An increase in the number of cases can also be because of increased vigilance and improved detection rather than an increase in morbidity. Time trend analysis of rheumatic fever rates is probably only meaningful at a regional or national level and it is not covered in this report.

Despite these limitations the following key points can be made:

. For the 2009-2013 periods there was an average of 8.8 cases per year for Bay of Plenty DHB and 7.6 per year for Lakes DHB. These figures are similar to the Ministry of Health targets for 2012/13 of eight for Bay of Plenty DHB and seven for Lakes DHB3.

. Rheumatic fever rates within the Toi Te Ora – Public Health Service (Toi Te Ora) area are highest in the Eastern Bay of Plenty and in Rotorua. There are also some small areas that have high rates in other parts of the Toi Te Ora area.

. Over 80% of cases were Maori with this proportion higher for Bay of Plenty DHB (86%) than for Lakes DHB (79%). The highest proportion of cases that were Maori were in Western Bay of Plenty, Opotiki, Whakatane and Rotorua Districts.

. Children aged 5-14 years are a key group with a high risk of rheumatic fever. For the Toi Te Ora area as a whole, 68% of cases were in this age group. This figure was higher for Bay of Plenty DHB (73%) compared with Lakes DHB (63%). The highest proportions of cases that were children aged 5-14 were in Opotiki, Whakatane and Taupo Districts.

. The proportion of cases that were children aged 5-14 (68%) is lower than was found in previous analysis in 2013 for the 2007-2011 periods (72%). In recent years there have been more cases aged 15 or older.

Introduction

This document summarises recent information on hospital admissions for rheumatic fever for residents of the Bay of Plenty and Lakes District Health Board areas. It is based on data provided to Toi Te Ora by the Ministry of Health showing “initial admissions” to hospital for rheumatic fever in the period from 2009-2013. “Initial admissions” means the first time a person has been admitted to hospital for rheumatic fever and the Ministry of Health looks back over more than 20 years of public hospital admission data to calculate this.

International Classification of Disease (ICD10) codes are used to define rheumatic fever hospitalisations. This data is the basis of the information that the Ministry of Health uses for monitoring the rheumatic fever Better Public Services Target and the definition of which hospital admissions are included or excluded is clarified below4.

Included . Overnight admissions and day case admissions with a principal diagnosis of acute rheumatic fever (ICD10 codes I00, I01, I02).

Excluded . People with a previous acute rheumatic fever diagnosis admission (principal and additional) from 1988 onwards.

. People with a previous chronic rheumatic heart disease diagnosis admission (principal and additional) from 1988 onwards (ICD10 codes 105- 109).

. Non-residents of New Zealand.

Number of Rheumatic Fever Hospital Admissions

This data shows that there were 82 initial hospitalisations for rheumatic fever for people resident in the Toi Te Ora area in the 5 years from 2009 to 2013. Of this total 44 were from the Bay of Plenty DHB area and 38 were from the Lakes DHB area.

This is an average of 8.8 per year for Bay of Plenty DHB and 7.6 per year for Lakes DHB. These figures are similar to the Ministry of Health targets of eight for 2012/13 and seven for 2013/14 for both the Bay of Plenty and Lakes DHBs5.

Overall 83% of cases were Maori with this proportion higher for Bay of Plenty DHB (86%) than for Lakes DHB (79%). This is much higher than the proportion of the population who are Maori and clearly shows the over-representation of Maori in rheumatic fever statistics.

Overall 68% of cases were children aged 5-14 years with this proportion higher for Bay of Plenty DHB (73%) than for Lakes DHB (63%).

For children aged 5-14 years 86% of cases were Maori with this proportion higher for Bay of Plenty DHB (88%) than for Lakes DHB (83%).

More detailed data showing the number of rheumatic fever cases is provided in the tables in Appendix 1.

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Rheumatic Fever Rates

Data showing admissions to hospital for rheumatic fever in the period from 2009-2013 were used to calculate rheumatic fever hospitalisation rates for Bay of Plenty and Lakes DHBs.

This information was provided by the Ministry of Health and was used as the numerators for rate calculations. Census data from 2006 and 2013 were used as the basis for calculating denominator populations used in the rate calculations. Linear interpolation was used to estimate the population for the 2009-2013 periods. The data used in the rate calculations is shown in Appendix 2.

The populations from the 2013 Census were lower than expected for most local authorities within the Toi Te Ora area (based on population projection data). This means that most denominators used in these rate calculations are lower compared with those used for an earlier report produced by Toi Te Ora for the 2007-2011 period. The earlier report was also based on an approximation to the Ministry of Health definition of “first hospitalisation for rheumatic fever” while this report is based on official Ministry of Health data. For these reasons, the rates from this report cannot be meaningfully compared with the rates from the earlier report.

Rates were calculated for the total population and Maori for people of all ages and for 5-14 year olds. 95% Confidence Intervals were used to give an idea of the precision of the calculated rates and to indicate whether or not observed differences are statistically significant. Normal distribution confidence intervals were used for data at District Health Board level and Poisson distribution confidence intervals were used for data at local authority level.

Where there are a small number of events confidence intervals can be quite wide. For example, for Maori living in the Bay of Plenty DHB area, the calculated rate was 16.2 per 100,000 but the confidence interval ranges from 11.1 to 21.4. This means we can be 95% sure that the true rate is between 11.1 and 21.4. The confidence intervals are much wider for smaller populations (e.g. District). When comparing groups, if confidence interval ranges overlap, then observed differences are not statistically significant.

Rates for the Overall Population

This analysis showed that:

. For both DHBs the Maori rate was significantly greater than the rate for the overall population

. Although the rate for Lakes DHB was higher than the rate for Bay of Plenty DHB this difference was not statistically significant

First Hospital Admission for Rheumatic Fever Rate/100,000 and 95% Confidence Interval BOPDHB and Lakes DHB, 2009-2013

DHB Maori Total 16.2 4.3 BOPDHB (11.1 – 21.4) (3.1 – 5.6) 19.1 7.7 Lakes DHB (12.3 – 25.9) (5.3 – 10.2)

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Rheumatic fever rates were also calculated at local authority level to analyse patterns across the Toi Te Ora area. In many cases the number of events was too small at this level of analysis to detect statistically significant differences, even with five years of data aggregated.

This data shows that:

. In all areas Maori have a higher rheumatic fever rate than the overall population but this difference was only statistically significant for Rotorua District and City.

. For areas with small populations it is generally less likely that differences between groups will be statistically significant because the number of events is small and confidence intervals are wide. Therefore even when a difference between groups appears to be large, the difference still fails to reach statistical significance (e.g. for Opotiki District the Maori rate was nearly twice the total population rate but this difference was not statistically significant).

. Rates are generally higher in Eastern Bay of Plenty areas (Whakatane, Kawerau and Opotiki) and Rotorua compared with Western Bay of Plenty areas (Tauranga City and Western Bay of Plenty District). Some of these differences are statistically significant for the overall population. The Taupo rate is intermediate between Western Bay of Plenty areas and Rotorua/Eastern Bay of Plenty areas.

First Hospital Admission for Rheumatic Fever Rate/100,000 and 95% Confidence Interval By Local Authority, 2009-2013

Local Maori Total Authority 8.1 1.4 Western BOP (1.7 – 23.8) (0.3 – 4.1) 8.9 2.1 Tauranga (3.8 – 17.4) (1.1 - 3.8) 27.5 11.6 Whakatane (16.3 – 43.5) (7.0 – 18.1) 16.5 12.3 Kawerau (3.4 – 48.2) (3.3 - 31.4) 26.0 14.0 Opotiki (9.5 – 56.5) (5.1 – 30.4) 13.5 4.9 Taupo (4.9 - 29.3) (2.1 – 9.6) 21.3 9.2 Rotorua (13.7 - 31.7) (6.2 – 13.1)

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The graphs below show the rheumatic fever rates for the total population and for Maori. Both simple bar graphs and graphs showing confidence intervals are provided.

Graph Showing Overall Rheumatic Fever Rate by Local Authority Area

Graph Showing Overall Rheumatic Fever Rate by Local Authority Area with 95 % Confidence Intervals

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Graph Showing Maori Rheumatic Fever Rate by Local Authority Area

Graph Showing Maori Rheumatic Fever Rate by Local Authority Area with 95% Confidence Interval

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Rates for Children aged 5-14 years

Children aged 5-14 years are a key group with high risk of rheumatic fever. Hospitalisation data showed that in the 2009-2013 period 73% of Bay of Plenty DHB cases and 63% of Lakes DHB cases were in this age group. Rheumatic fever rates were therefore calculated specifically for this group. This analysis showed that:

. For both DHBs the rate for Maori children aged 5-14 years was greater than the rate for all children but this difference was only statistically significant for Bay of Plenty DHB.

. For children aged 5-14 years the rate for Lakes DHB was higher than the rate for Bay of Plenty DHB but this difference was not statistically significant.

. The rheumatic fever rate for Maori children aged 5-14 years is quite similar for the two DHBs.

First Hospital Admission for Rheumatic Fever Rate/100,000 and 95% Confidence Interval Age 5-14 Years, BOPDHB and Lakes DHB, 2009-2013

DHB Maori Total 51.7 21.5 BOPDHB (32.5 – 70.8) (14.1 – 29.0) 56.8 31.4 Lakes DHB (31.9 – 81.7) (18.9 – 44.0)

Rheumatic fever rates were calculated at local authority level to analyse patterns across the Bay of Plenty and Lakes Districts. The number of events was generally too small at this level of analysis to detect statistically significant differences even with five years of data aggregated. It is possible however to make some general observations from this data.

. In all areas except Kawerau, Maori children aged 5-14 have a higher rheumatic fever rate than the rate for all children aged 5-14.

. For areas where a very high proportion of the population are Maori (e.g. Kawerau) the difference between the rate for Maori children and the rate for all children is less.

. Rates are generally higher in Eastern Bay of Plenty areas (Whakatane, Kawerau and Opotiki) and Rotorua compared with Western Bay of Plenty areas (Tauranga City and Western Bay of Plenty District). The Taupo rate is intermediate between Western Bay of Plenty areas and Rotorua/Eastern Bay of Plenty areas.

. Some of the differences between districts were statistically significant. (E.g. The overall rate for Whakatane District children was significantly higher than the overall rates for Western Bay of Plenty and Tauranga children).

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First Hospital Admission for Rheumatic Fever Rate/100,000 and 95% Confidence Interval Age 5-14 Years, By Local Authority, 2009-2013

Local Maori Total Authority 23.7 6.4 Western BOP (2.9 – 85.6) (0.8 – 23.1) 28.3 10.3 Tauranga (10.4 – 61.5) (4.5 – 20.4) 92.4 55.4 Whakatane (50.5 – 155.0) (31.0 – 91.4) 23.8 34.6 Kawerau (0.6 – 132.5) (4.2 – 124.9) 96.3 68.5 Opotiki (31.3 – 224.7) (22.2 – 159.8) 51.9 25.3 Taupo (16.9 – 121.2) (9.3 – 55.0) 58.7 34.2 Rotorua (32.8 – 96.7) (20.3 – 54.1)

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The graphs below show the rheumatic fever hospitalisation rates for the total population of children aged 5-14 years and for Maori children in this age group. Both simple bar graphs and graphs showing confidence intervals are provided.

Graph Showing Rheumatic Fever Rate for Children by Local Authority Area

Graph Showing Rheumatic Fever Rate for Children by Local Authority Area with Confidence Intervals

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Graph Showing Rheumatic Fever Rate for Maori Children by Local Authority Area

Graph Showing Rheumatic Fever Rate for Maori Children by Local Authority Area with 95% Confidence Intervals

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Conclusion

This analysis has shown that the average number of first hospitalisations for rheumatic fever per year for the 2009-2013 periods was similar to the Ministry of Health targets for the 2012/13 financial year. The challenge is to reduce these numbers by 2017.

This report provides an update on the number of first hospitalisations, the distribution of cases and the rates for different subsets of the population. This may assist with targeting efforts to reduce rheumatic fever in the Bay of Plenty and Lakes DHB areas.

Rheumatic fever rates within the Toi Te Ora area are highest in the Eastern Bay of Plenty and in Rotorua. There are also some small areas that have high rates in other parts of the Toi Te Ora area.

Most rheumatic fever cases are Maori and children aged 5-14 years are a key group with a high risk of rheumatic fever. The proportion of cases that were children aged 5-14 is slightly lower than was found in previous analysis and in recent years there have been more cases aged 15 or older.

The most recent calendar year data appears to show an increase in the number of initial hospitalisations for rheumatic fever for the Bay of Plenty DHB in 2013. However it is important to not read too much into this. There are several reasons why a higher number of cases are apparent.

Rheumatic fever numbers fluctuate year to year and with the small number of cases each year a change in the period analysed can influence the perception of the number of cases. For example, for the Bay of Plenty DHB there were 13 cases in the 2008/09 financial year and only seven in the 2012/13 financial year which may appear to suggest a decline. Conversely there were seven cases in the 2009 calendar year and 14 in 2013 which may appear to suggest an increase.

With the amount of focus on rheumatic fever in recent years, increased government funding and programmes aimed at early detection there may be greater case ascertainment and detection of cases that may have previously gone undetected which gives the appearance of an increase in the disease itself. The Minister of Health has recently stated that “the international research indicates that increased awareness means the number of cases reported will go up before it comes down”6.

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Appendix 1

Summary of Rheumatic Fever Initial Hospitalisation Data

First Hospitalisation for Rheumatic Fever 2009-2013 (Total Population)

Local 5-14 years % 5-14 All ages Authority years Western BOP 2 3 66.7% Tauranga 8 12 66.7% Whakatane 15 19 78.9% Kawerau 2 4 50.0% Opotiki 5 6 83.3% BOPDHB 32 44 72.7% Taupo 6 8 75.0% Rotorua 18 30 60.0% Lakes DHB 24 38 63.2%

First Hospitalisation for Rheumatic Fever 2009-2013 (Maori)

Local 5-14 years % 5-14 All ages Authority years Western BOP 2 3 66.7% Tauranga 6 8 75.0% Whakatane 14 18 77.8% Kawerau 1 3 33.3% Opotiki 5 6 83.3% BOPDHB 28 38 73.7% Taupo 5 6 83.3% Rotorua 15 24 62.5% Lakes DHB 20 30 66.7%

Proportion of Rheumatic Fever Initial Hospitalisation Cases that are Maori compared with Proportion of the Population that are Maori, 2009-2013

Proportion of Initial Proportion of the Hospitalisations population that are for Rheumatic Maori (%) Fever that are Maori (%) All Ages BOPDHB 86 23 Lakes DHB 79 32 Toi Te Ora 83 26

5-14 years BOPDHB 88 37 Lakes DHB 83 46 Toi Te Ora 86 40

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Appendix 1 (continued)

Summary of Rheumatic Fever Initial Hospitalisation Data

First Hospitalisations for Rheumatic Fever BOPDHB and Lakes DHB, 2009-2013 Calendar Years

2009 2010 2011 2012 2013* Total

BOPDHB 7 8 9 6 14 44 Lakes DHB 9 5 7 10 7 38 TTO 16 13 16 16 21 82

First Hospitalisations for Rheumatic Fever BOPDHB and Lakes DHB, 2009-2013 Financial Years

2008/2009 2009/2010 2010/2011 2011/2012 2012/2013 Total BOPDHB 13 6 7 11 7 44 Lakes 8 6 5 13 7 39 DHB TTO 21 12 12 24 14 83

First Hospitalisations for Rheumatic Fever BOPDHB and Lakes DHB, 2012-2017 Financial Years, Ministry of Health Targets

2012/2013 2013/2014 2014/2015 2015/2016 2016/2017 BOPDHB 8 7 5 4 3 Lakes DHB 8 7 5 4 3 TTO 16 14 10 8 6

Notes

Initial hospitalisation data is based on data provided by the Ministry of Health showing initial hospitalisations for rheumatic fever between 2009 and 2013.

Data for the latest year should be regarded as provisional because totals could change slightly after coding is reviewed.

Population data used was the estimated population for the 2009-2013 period based on linear interpolation of figures from the 2006 and 2013 Census.

The Ministry of Health target data above is from a document produced by the Ministry of Health summarising guiding information for District Health Boards with a high incidence of acute rheumatic fever hospitalisations produced in July 2013.

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Appendix 2

Data Used for Calculation of Rheumatic Fever Rates Total Population (All Ethnic Groups)

First Hospitalisation for Rheumatic Fever and Estimated Average Annual Population 2009 – 2013, All Ages

Local First Hospitalisation for RF Average Annual Authority 2009-2013 Combined Population Western BOP 3 43162 Tauranga 12 111672 Whakatane 19 32862 Kawerau 4 6522 Opotiki 6 8588 BOPDHB 44 202807 Taupo 8 32767 Rotorua 30 65457 Lakes DHB 38 98224

First Hospitalisation for Rheumatic Fever and Estimated Average Annual Population 2009 – 2013, Children Aged 5-14 Years

Local First Hospitalisation for RF Average Annual Authority 2009-2013 Combined Population Western BOP 2 6242 Tauranga 8 15462 Whakatane 15 5415 Kawerau 2 1157 Opotiki 5 1460 BOPDHB 32 29735 Taupo 6 4749 Rotorua 18 10517 Lakes DHB 24 15265

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Appendix 2 (continued)

Data Used for Calculation of Rheumatic Fever Rates: Maori

First Hospitalisation for Rheumatic Fever and Estimated Average Annual Population 2009 – 2013, Maori, All Ages

Local First Hospitalisation for RF Average Annual Authority 2009-2013 Combined Population Western BOP 3 7378 Tauranga 8 18075 Whakatane 18 13081 Kawerau 3 3641 Opotiki 6 4623 BOPDHB 38 46798 Taupo 6 8920 Rotorua 24 22503 Lakes DHB 30 31423

First Hospitalisation for Rheumatic Fever and Estimated Average Annual Population 2009 – 2013, Maori Children Aged 5-14 Years

Local First Hospitalisation for RF Average Annual Authority 2009-2013 Combined Population Western BOP 2 1688 Tauranga 6 4243 Whakatane 14 3029 Kawerau 1 840 Opotiki 5 1038 BOPDHB 28 10839 Taupo 5 1926 Rotorua 15 5115 Lakes DHB 20 7041

Prepared by:

Stephen Twitchin Public Health Analyst Health Services Development Toi Te Ora – Public Health Service

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References

1 Ministry of Health (2013) Rheumatic Fever Retrieved from http://www.health.govt.nz/our- work/diseases-and-conditions/rheumatic-fever

2 Ministry of Health (2013) Better Public Services Retrieved from http://www.health.govt.nz/about-ministry/what-we-do/strategic-direction/better-public- services

3 Ministry of Health (2013) Rheumatic fever prevention plans: Guiding information for District Health Boards with a high incidence of acute rheumatic fever hospitalisations. Wellington.

4 Ministry of Health (2013) Reduce rheumatic fever progress Retrieved from http://www.health.govt.nz/about-ministry/what-we-do/strategic-direction/better-public- services/reduce-rheumatic-fever-progress

5 Ministry of Health (2013) Rheumatic fever prevention plans: Guiding information for District Health Boards with a high incidence of acute rheumatic fever hospitalisations. Wellington.

6 Minister of Health (2014) Address to Waitemata Lecture Series. 25 March 2014. Retrieved from http://www.national.org.nz/Article.aspx?articleId=43452

Respiratory infection document: G:\Toi Te Ora\Z_WORKING\Planning\Goal 1 - Childhood Infections\Resp Infection Hospitalisation Summary 2014.docx

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