The Epidemiology of Meningococcal Disease in New Zealand in 2005

The Epidemiology of

Meningococcal Disease

in New Zealand in 2005

Martin D, Lopez L, McDowell R. 2006. The Epidemiology of Meningococcal Disease in New Zealand in 2005. Report prepared for the Ministry of Health by the Institute of Environmental Science and Research Limited (ESR). Wellington: Ministry of Health.

Published in June 2006 by the

Ministry of Health

PO Box 5013, Wellington, New Zealand

ISBN: 0-478-29999-0 (Book)

ISBN: 0-478-29956-7 (Internet)

HP 4127

This document is available on the Ministry of Health’s website:

http://www.moh.govt.nz

Meningococcal Disease in

New Zealand in 2005

Prepared as part of the Ministry of Health

contract for scientific services (Project C5)

May 2006

Client Report

FW 0628

Meningococcal Disease in

May 2006

Diana Martin

Principal Scientist

Programme and Project Leader, Communicable Disease

DISCLAIMER

This report or document (“the Report”) is given by the Institute of Environmental Science and Research Limited (“ESR”) solely for the benefit of the Ministry of Health, Public Health Service Providers and other Third Party Beneficiaries as defined in the Contract between ESR and the Ministry of Health, and is strictly subject to the conditions laid out in that contract.

Neither ESR nor any of its employees makes any warranty, express or implied, or assumes any legal liability or responsibility for use of the Report or its contents by any other person or organisation.

AcknowleDgements

This report could not have been generated without the continuing support of staff in Public Health Services, clinical laboratories, medical practices and hospitals throughout New Zealand. All have a role in improving surveillance. The authors wish to especially thank Heather Davies, Moana Ngatai, and Daniel Kay for meningococcal specialist laboratory testing; Carol Kliem and Trev Margolin for data integration, Toby Regan for the maps, Aloka Maitra for statistical advice, Kerry Sexton, Robbie Lane, and Yvonne Galloway for peer review.

The Epidemiology of Meningococcal Disease May 2006

in New Zealand in 2005

CONTENTS

Executive Summary i

1. Introduction 1

2. Methods 2

2.1. Surveillance Methods 2

2.2. Laboratory Methods 4

3. Results 5

3.1. Incidence and Distribution 5

3.1.1. Incidence by Year and Month 5

3.1.2. Incidence by Place 8

3.1.3. Incidence by Age 10

3.1.4. Incidence by DHB and Age Group 12

3.1.5. Incidence by Ethnicity 12

3.1.6. Incidence by DHB and Ethnicity 13

3.1.7. Incidence by Gender 14

3.1.8. Incidence by Deprivation (NZDep2001) 14

3.2. Basis for Diagnosis 16

3.2.1. Clinical Description 16

3.2.2. Confirmation of Disease Based on Laboratory Testing 16

3.2.3. Impact of Pre-hospital Antibiotic Treatment on Confirmation of Disease by Culture 17

3.2.4. Confirmation of Disease by PCR Testing Following Antibiotic Usage 18

3.2.5. Geographical, Ethnic and Age Group Disparities in the Confirmation of Disease 18

3.2.6. Characteristics of Meningococci Causing New Zealand’s Disease 20

3.2.7. Cases Confirmed by Isolation of a Meningococcus 20

3.2.8. Cases Confirmed by PCR Alone 20

3.2.9. Overall Burden of Disease 21

3.2.10. Antimicrobial Susceptibility 21

3.3. Clinical Outcome 23

3.3.1. Case-fatality 23

3.4. Case Management 24

3.4.1. Hospitalisation 24

3.4.2. Pre-hospital Visit to Doctor and Antibiotic Treatment 24

3.4.3. Pre-hospital Antibiotic Treatment by Age Group 25

3.5. Risk Factors 26

3.5.1. Contact with Case 26

4. Discussion 27

Appendix 29

References 44

LIST OF FIGURES

Figure 1: New Zealand meningococcal disease surveillance system, showing main information flows and integration of laboratory and notification information sources 3

Figure 2: Confirmed and probable notified meningococcal disease cases, 1990-2005 5

Figure 3: Meningococcal disease cases for Norway, 1971-1990 6

Figure 4: Meningococcal disease cases in New Zealand, 1989-2005 6

Figure 5: Meningococcal disease cases by month, 2001-2005 7

Figure 6: Meningococcal disease cases and influenza isolates by month, 2001-2005 7

Figure 7: Meningococcal disease rates by District Health Board, 2005 8

Figure 8: Meningococcal disease rates per 100 000 by District Health Board, 2005 9

Figure 9: Meningococcal disease rates per 100 000 by District Health Board, 2001-2005 10

Figure 10: Meningococcal disease rates by age group, 2001-2005 11

Figure 11: Meningococcal disease cases by age, 2005 11

Figure 12: Age standardised rates for meningococcal disease cases by ethnicity, 2001-2005 12

Figure 13: Meningococcal disease rates by age group and ethnicity, 2005 13

Figure 14: Rates of meningococcal disease by age group and associated index of deprivation, 2005 15

Figure 15: Rates of meningococcal disease in North and South Islands District Health Boards by associated index of deprivation, 2005 15

Figure 16: Meningococcal disease cases by District Health Board for PCR and other means of confirmation, 2005 19

Figure 17: Meningococcal disease isolate serogroup and dominant subtype, 1990-2005 20

Figure 18: Meningococcal disease percentage of confirmed cases (isolate and/or PCR) with epidemic strain type by year, 1990-2005 21

Figure 19: MIC of isolates with reduced susceptibility to penicillin among meningococci from invasive disease, 1996-2005 22

Figure 20: Meningococcal disease case-fatality rates, 1991-2005 23

LIST OF TABLES

Table 1: Recorded clinical description for meningococcal disease cases, 2001-2005 16

Table 2: Meningococcal disease, basis for diagnosis, 2001-2005 17

Table 3: Pre-hospital antibiotic treatment and isolation of viable organisms from cases of meningococcal disease, 2005 17

Table 4: Pre-hospital antibiotic treatment of meningococcal disease cases by basis of laboratory confirmation, 2005 18

Table 5: Pre-hospital antibiotic treatment and isolation of viable organisms from cases of meningococcal disease, 2001-2005 17

Table 6: MIC range and MIC90 of isolates, 2005 22

Table 7: Meningococcal disease outcome in relationship to being seen by a doctor and receiving pre-hospital antibiotic treatment, 2005 24

Table 8: Meningococcal disease outcome in relationship to being seen by a doctor and receiving pre-hospital antibiotic treatment, 2001-2005 25

Table 9: Pre-hospital antibiotic treatment of meningococcal disease cases by age group, 2005 25

Table 10: Relationship between associated cases of meningococcal disease and suspected index case, 2005 26

Table 11: Numbers and rates for cases of meningococcal disease by District Health Board, 2001-2005 29

Table 12: Geographic distribution by District Health Board of confirmed cases of meningococcal disease and proportion of confirmed to total cases, 2001-2005 30

Table 13: Age distribution of meningococcal disease cases, 2001-2005 31

Table 14: Age group distribution for confirmed cases of meningococcal disease and proportion of confirmed to total cases, 2001-2005 31

Table 15: Meningococcal disease cases, less than five year olds versus those age five years and over, 1990-2005 32

Table 16: Age distribution by months for total and confirmed cases of meningococcal disease aged 0-24 months, 2005 and 2001-2005 33

Table 17: Numbers and rates for cases of meningococcal disease by age group and District Health Board, 2005 34

Table 18: Numbers and age-standardised incidence rates by ethnicity for cases of meningococcal disease, 2001-2005 35

Table 19: Ethnicity distribution of confirmed cases of meningococcal disease and proportion of confirmed to total cases, 2001-2005 35

Table 20: Numbers and crude incidence rates for cases of meningococcal disease by age group and ethnicity, 2005 36

Table 21: Age group and ethnicity distribution for confirmed cases of meningococcal disease by age group and ethnicity, 2005 36

Table 22: Numbers and rates for cases of meningococcal disease by ethnicity for District Health Board, 2005 37

Table 23: Gender distribution of meningococcal disease cases, 2001-2005 37

Table 24: Gender distribution of confirmed cases of meningococcal disease and proportion of confirmed to total cases, 2001-2005 37

Table 25: Cases of meningococcal disease by District Health Board for PCR and other means of confirmation, 2005 38

Table 26: Cases of meningococcal disease by age group and District Health Board for PCR and other means of confirmation, 2005 39

Table 27: Distribution of meningococcal isolate and PCR results defined by serotyping or DNA sequence analysis, 2005 39

Table 28: Distribution of meningococcal isolate and PCR results defined by serotyping or DNA sequence analysis by DHB, 2005 40

Table 29: Case-fatality rates for meningococcal disease cases by age, gender, ethnicity, serogroup, clinical description and basis, 2001-2005 41

Table 30: Case-fatality rates for confirmed cases meningococcal disease by age, gender, ethnicity and clinical description, 2001-2005 42

Table 31: Follow-up of contacts of meningococcal disease cases, 2005 43

Table 32: Total number of contacts identified and offered counselling, antibiotics and vaccination, 2005 43

The Epidemiology of Meningococcal Disease May 2006

in New Zealand in 2005

Executive Summary

Introduction

§ Reviews of meningococcal disease epidemiology in New Zealand have variously been published since 1991. This report provides 2005 data and some comparative historic data.

Surveillance Methods

§ Surveillance of meningococcal disease is based on the combination of disease notification and laboratory data. Isolates and/or meningococcal DNA from cases of disease are fully characterised enabling monitoring and reporting of disease incidence by group and strain type.

Incidence and Distribution

§ A total of 228 cases of meningococcal disease were notified in 2005, a rate of 6.1 per 100 000, the lowest since 1994. Of the 228 cases, 87.7% (200) were laboratory confirmed, the highest confirmation rate since 1994. The total number of cases since the start of the epidemic in 1991 is 5863, with 238 deaths recorded, a case fatality rate of 4.1%. The case fatality rate for 2005 was 6.1% (14 deaths), the highest rate since the start of the epidemic, although the number of deaths is less than the epidemic average of 16. The impact of giving antibiotics prior to hospital admission was again shown by the lower case fatality rate in those receiving antibiotics. A higher case fatality rate for group C disease (11.0%) than group B disease (3.3%) has been observed over the last five years.

§ Throughout the epidemic, highest case numbers have consistently been in the upper North Island, particularly in the Counties Manukau, Waitemata and Auckland District Health Boards (DHBs). However in 2005 there were only 30 cases in Counties Manukau DHB compared with an average of 81 cases over the previous three years. Of the DHBs reporting over 10 cases, only Waikato had more cases in 2005 than in 2004 (33 versus 23 respectively).

§ The delivery of MeNZBä vaccine as part of the Meningococcal B Immunisation Programme began in the Counties Manukau DHB and some eastern suburbs of Auckland DHB in July 2004. Over the first half of 2005, the Programme was progressively implemented around the country (according to historical disease burden) and expanded to cover all aged between 6 weeks and 19 years. The last DHB (Nelson Marlborough) became eligible to vaccinate in July 2005.

§ As at the end of December 2005, just over three quarters (75.6%) of the eligible population of people aged 6 weeks to 19 years of age had received their third dose of vaccine.

§ The MeNZB™ vaccine only targets the epidemic strain with PorA type P1.7b,4. Background rates of disease of other serogroups and subtypes will continue.

§ The rate per 100 000 population for all meningococcal disease in 2005 showed a significant decrease (chi-square=22.8, p<0.0001) on the rate for 2004 (9.2 per 100 000 population, 342 cases) and was the lowest since 1994 (5.7 per 100 000 population, 207 cases).

§ The highest age-specific rates of disease continue to be in children less than five years of age, although the rates were less than that seen in preceding years; 53.1 per 100 000 for those aged less than one year and 18.0 per 100 000 for 1-4 year olds. The correlation of high rates of disease with age of children less than 5 years and increasing deprivation was again shown in 2005.

§ Since at least 1996, the risk of contracting meningococcal disease over the epidemic has consistently been highest in Pacific and Maori communities. Ethnicity based age-standardised rates have varied from year to year. In 2005, the rates for Pacific Peoples and Maori were 2.3 and 1.7 times higher than those of European ethnicity. In 2005, for those aged less than 10 years of age the rates for Pacific Peoples and for Maori were significantly higher (chi square=36.7, <0.0001 and 31.2 p<0.0001 respectively) when compared with European children of the same age. In 2005, the rate for children of Pacific Peoples ethnicity aged under one year was 58.2 per 100 000 population, around a third of the 2004 rate of 174.5 and almost 9 times less than the 2003 rate (504.2 per 100 000). In 2005, in the under one age group, the Maori rate was higher than the Pacific rate for the first time since at least 1996, but less than the Maori rate for 2004.

§ In 2005, disease confirmation rates for Auckland, MidCentral, and Otago DHBs were noticeably higher than in 2004. Auckland DHB’s overall confirmation of meningococcal disease increased from 55.3% (21 cases) in 2004 (the national low) to 81.3% (13 cases) in 2005. Use of PCR nationally increased the confirmation rate by 35.0% (70/200); highlighting the importance of PCR to laboratory confirm meningococcal disease. Geographical disparity in the use of PCR has impacted on confirmation rates particularly in previous years and in areas with higher numbers of cases.

§ In 2005, group B meningococci continued to dominate throughout New Zealand causing 77.9% (148/190) of all cases that could be typed. However, the number of epidemic strain decreased in 2005, with the proportion among all typed cases decreasing to 59.5% (113/190). This was significantly lower (chi-square=9.01, p<0.0027) than in 2004 when the epidemic strain was responsible for 73.0% (184/252) of all cases that could be typed. Group C meningococci represented 15.8% (30/190) of all cases. Capsular type W135 meningococci occurred in 8 cases in 2005 (9 cases in 2004). In view of the reduced penicillin susceptibility observed among the W135 isolates it will be important to monitor this capsular type.

Discussion and Implications

§ Accurate disease surveillance data including evidence of disease confirmation are vital for the evaluation of the effectiveness of the MeNZBä vaccine in combating the meningococcal disease epidemic in New Zealand. The established robust historical dataset provides the information against which changes in disease epidemiology can be evaluated. The number and proportion of meningococcal cases caused by the epidemic strain decreased significantly in 2005, presumed to be associated at least in part with delivery of the vaccine.