An overview of the epidemiology of notifiable infectious diseases in Australia, 1991–2011

An overview of the epidemiology of notifiable infectious diseases
in Australia, 1991–2011
K. B. GIBNEY*, A. C. CHENG, R. HALL AND K. LEDER
Department of Epidemiology and Preventive Medicine, Monash University, The Alfred Centre, Melbourne,
Victoria, Australia
Received 24 February 2016; Final revision 28 April 2016; Accepted 5 May 2016;
first published online 22 June 2016
SUMMARY
We reviewed the first 21 years (1991–2011) of Australia’s National Notifiable Diseases
Surveillance System (NNDSS). All nationally notified diseases (except HIV/AIDS and
Creutzfeldt–Jakob disease) were analysed by disease group (n = 8), jurisdiction (six states
and two territories), Indigenous status, age group and notification year. In total, 2 421 134
cases were analysed. The 10 diseases with highest notification incidence (chlamydial infection,
campylobacteriosis, varicella zoster, hepatitis C, influenza, pertussis, salmonellosis, hepatitis B,
gonococcal infection, and Ross River virus infection) comprised 88% of all notifications. Annual
notification incidence was 591 cases/100 000, highest in the Northern Territory (2598/100 000) and
in children aged <5 years (698/100 000). A total of 8·4% of cases were Indigenous Australians.
Notification incidence increased by 6·4% per year (12% for sexually transmissible infections and
15% for vaccine-preventable diseases). The number of notifiable diseases also increased from 37
to 65. The number and incidence of notifications increased throughout the study period, partly
due to addition of diseases to the NNDSS and increasing availability of sensitive diagnostic tests.
The most commonly notified diseases require a range of public health responses addressing high-
risk sexual and drug-use behaviours, food safety and immunization. Our results highlight
populations with higher notification incidence that might require tailored public health
interventions.
Key words: Analysis of data, Australia, epidemiology, public health, surveillance system.
I N T RO D U C T I O N
Surveillance is the cornerstone of public health efforts
to minimize morbidity and mortality resulting from
preventable infectious diseases. Infectious disease sur-
veillance was instrumental in smallpox eradication
and in current efforts towards global polio eradication
and measles elimination. National surveillance sys-
tems allow examination of the epidemiological
profile of important infections at a country level and
provide oversight to ensure consistent reporting across
jurisdictions [1].
In Australia, notification of selected infectious dis-
eases is required by public health legislation in the
six states and two territories. Each jurisdiction
defines its own notification list and receives data
from doctors and/or laboratories. Primary responsibil-
ity for public health action lies with the state/territory
health departments. Jurisdictions forward de-identified
* Author for correspondence: Dr K. B. Gibney, The Peter Doherty
Institute for Infection and Immunity, 792 Elizabeth Street,
Melbourne 3000 Victoria, Australia.
(Email: [e-mail])
Epidemiol. Infect. (2016), 144, 3263–3277. © Cambridge University Press 2016
doi:10.1017/S0950268816001072
https://doi.org/10.1017/S0950268816001072
Downloaded from https:/www.cambridge.org/core. Kainan University, on 10 Feb 2017 at 06:18:55, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms.

notification data for cases meeting national case
definitions for diseases on the National Notifiable
Diseases List (NNDL) to the National Notifiable
Disease Surveillance System (NNDSS), a passive sur-
veillance system operational since 1991.
A summary of national notifiable disease surveil-
lance data from 1917 to 1991 highlighted the lack of
consistency, detail, and methodical reporting of na-
tionally notifiable diseases before the introduction of
the NNDSS [2]. Annual reports of NNDSS data
have been produced since 1991; however, trend ana-
lysis of all nationally notifiable diseases has not previ-
ously been performed. We present an overview of the
epidemiology of all notifiable infectious diseases in
Australia [excluding HIV/AIDS and Creutzfeldt–
Jakob disease (CJD)] during the first 21 years of the
NNDSS, with a view to highlighting diseases and
population groups with greatest need of public health
intervention to reduce disease incidence.
M E T H O D S
All case notifications of nationally notifiable diseases
to the NNDSS from 1 January 1991 to 31 December
2011 were analysed according to their diagnosis date
[3]. HIV/AIDS and CJD are under different national
surveillance systems and were excluded from this
analysis [4]. Notifications were reported by disease
and categorized into eight disease groups (as per the
NNDL) based on mode of acquisition and/or
public health strategies for control and prevention:
bloodborne viral hepatitis (BBVH), gastrointestinal,
other bacterial, quarantinable, sexually transmissible
infections (STIs), vector-borne diseases (VBDs),
vaccine-preventable diseases (VPDs), and zoonotic
diseases. Diseases included in each group and the
year they became notifiable are summarized in
Table 1. NNDSS diseases were analysed by pathogen
for hepatitis B, hepatitis C, rubella, syphilis, and vari-
cella zoster.
We report the number and annual incidence of
notified cases nationally and by jurisdiction. For all-
cause and disease-group incidence calculations, all
notified cases were included and Australian Bureau
of Statistics (ABS) population estimates at 30 June
for each study year were used [5]. Data from the
Northern Territory (NT) were excluded from both
the numerator (number of cases notified) and denom-
inator (population) of incidence calculations for 1994
due to large discrepancies between the study dataset
(extracted in 2012) and online (live) NNDSS data
that has undergone subsequent data cleaning [6]. For
disease-specific incidence calculations, diseases notifi-
able both nationally and in that jurisdiction were
included (Table 1) with the exceptions of hepatitis B
and C (Victoria 1991–1997), hepatitis B [South
Australian (SA) 1991–1995], tuberculosis (Victoria
1991), and varicella zoster (Victoria 2006–2007) due
to discrepancies with online NNDSS data; the denom-
inator comprised the combined populations for
included years and jurisdictions. Relative risks (RRs)
were calculated for univariate comparison of notifica-
tion incidence between study sub-periods (1991–1997,
1998–2004, 2005–2011), age groups (<5, 5–19, 20–64,
65–98 years) and jurisdictions for diseases with >400
notifications during the 21-year study period. Three
sub-periods were selected to allow more meaningful
comparison between disease groups/diseases within a
sub-period as well as analysis of change in notification
incidence across these sub-periods for a single disease
or disease group.
Average changes in annual notification incidence
over the study period were investigated by Poisson re-
gression for all diseases combined and by disease
group from 1991 to 2011; for individual diseases this
calculation was confined to years the disease was na-
tionally notifiable. Tests for statistical significance
were not performed as population-based data were
used. To allow international comparison, age-standar-
dized incidence rates were calculated using the WHO
world standard population distribution [7].
Incidence rates for Aboriginal and Torres Strait
Islander (‘Indigenous’) Australians were calculated
for the three jurisdictions reporting Indigenous status
for >75% of notified cases [NT, SA, and Western
Australia (WA)] using ABS population estimates
[8, 9]; cases with unknown Indigenous status were pre-
sumed non-Indigenous.
NNDSS data were provided by the Australian
Government’s Office of Health Protection on behalf
of Communicable Diseases Network Australia
(CDNA) jurisdictional members in March 2012 as
an extract from the national data file.
Ethical considerations
The project was approved by the Monash Human
Research Ethics Committee (project no. CF11/
2357–201) and CDNA jurisdictional members. Data
were analysed using Stata v. 12 (StataCorp., USA).
This work did not involve human or animal
experimentation.
3264 K. B. Gibney and others
https://doi.org/10.1017/S0950268816001072
Downloaded from https:/www.cambridge.org/core. Kainan University, on 10 Feb 2017 at 06:18:55, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms.

Table 1. Diseases included in the National Notifiable Diseases Surveillance System (NNDSS) by disease group and
year introduced, Australia 1991–2011
Year* Variation by jurisdiction
Bloodborne viral hepatitis
Hepatitis B (newly acquired) 1993 1994 in Qld and WA, 1995 in ACT
Hepatitis B (unspecified) 1991 2005 in NT
Hepatitis C (newly acquired) 1993 1995 in ACT, Tas and WA, 2005 in NT, not notifiable in Qld
Hepatitis C (unspecified) 1995 Included incident cases until hepatitis C newly acquired introduced
Hepatitis D 1999 2002 in WA
Hepatitis (NEC) 1991 2001 in WA. Included reports of hepatitis D and E 1991–1998
Gastrointestinal diseases
Botulism 1992 1993 in SA, 1998 in NT and NSW, 2001 in WA
Campylobacteriosis 1991† Not notifiable in NSW
Cryptosporidiosis 2001
Haemolytic uraemic syndrome 1999
Hepatitis A 1991†
Hepatitis E 1999 2001 in WA
Listeriosis 1991 1992 in SA, 1994 in NT
Salmonellosis (non typhoidal) 1991†
Shiga-/Vero-toxin-producing E. coli 1999 2001 in Qld and WA
Shigellosis 1991 2001 in NSW
Typhoid fever 1991† Includes paratyphoid in NSW, Qld and Vic
Quarantinable diseases
Cholera 1991†
Highly pathogenic avian influenza (human) 2004 Reported under influenza in WA
Plague 1991†
Rabies 1991 1993 in ACT, 1997 in NSW
Severe acute respiratory syndrome 2003
Smallpox 2004
Viral haemorrhagic fever 1991 1993 in ACT
Yellow fever 1991†
Sexually transmissible infections
Chancroid 1991 No longer nationally notifiable from 2000
Chlamydial infection 1994 1999 in NSW
Donovanosis 1991 1993 in Tas, 2002 in NSW and SA
Gonococcal infection 1991†
Syphilis 1991 Includes syphilis <2 and >2 years/unknown duration to 2004
Syphilis (<2 years duration) 2004
Syphilis (>2 years or unknown duration) 2004 Not reported in SA
Syphilis (congenital) 1991†
Vaccine-preventable diseases
Diphtheria 1991†
Haemophilus influenzae type b 1991 1994 in WA
Influenza (laboratory confirmed) 2001 2008 in SA
Measles 1991†
Mumps 1995 Not reported by Qld in 1995–96, 1999–2000
Pertussis 1991†
Pneumococcal disease (invasive) 2001
Poliomyelitis 1991†
Rubella 1993 1995 in Tas
Rubella (congenital) 1991†
Tetanus 1991 1994 in Qld
Varicella zoster (chickenpox) 2006 Not notifiable in NSW
Varicella zoster (shingles) 2006 Not notifiable in NSW
Varicella zoster (unspecified) 2006 Not notifiable in NSW
Notifiable diseases, Australia 1991–2011 3265
https://doi.org/10.1017/S0950268816001072
Downloaded from https:/www.cambridge.org/core. Kainan University, on 10 Feb 2017 at 06:18:55, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms.

R E S ULTS
The NNDSS contains 2 421 134 notified cases of 60
diseases from 1991 to 2011. STIs were most common
[790 990 (32·7%) notifications] and quarantinable dis-
eases least common (79 notifications, all cholera)
(Table 2, Fig. 1). Chlamydial infection, notifiable
from 1994, was the most commonly notified disease
[621 431 (26%) notifications]. The 10 pathogens
with highest notification incidence were Chlamydia
trachomatis, Campylobacter, varicella zoster virus,
hepatitis C virus, influenza virus, Bordetella pertussis,
Salmonella, hepatitis B virus, Neisseria gonorrhoeae,
and Ross River virus (RRV) (Tables 3 and 4); these
comprised 88% of all notifications despite campylo-
bacteriosis and varicella zoster infection not being
notifiable in New South Wales (NSW), the most
populous state. Fewer than 20 notifications were
received for eight diseases and no notifications were
received for seven diseases (Table 3).
Notification numbers increased over the study per-
iod, from 43 443 in 1991 (37 notifiable diseases) to
238 164 in 2011 (65 notifiable diseases) (Fig. 1). The
national annual notification incidence increased by
an average of 6·4% per year (Fig. 2), rising from
386/100 000 in the earliest sub-period (1991–1997) to
853/100 000 in the latest sub-period (2005–2011)
(Table 3). Annual notification incidence fell most
markedly for rubella (average 30% decrease/year), fol-
lowed by Haemophilus influenzae type B (Hib, 25%),
measles (23%), and donovanosis (17%) (Table 3).
Rubella and hepatitis A were among the 10 highest in-
cidence diseases in the earliest study sub-period
(Table 4). Conversely, influenza (average 33%
Table 1 (cont.)
Year* Variation by jurisdiction
Vector-borne diseases
Arbovirus infection (Not elsewhere
classified)
1991 1991–2000 included Japanese encephalitis, Kunjin, and Murray
Valley encephalitis (MVE) notifications
Barmah Forest virus infection 1995
Dengue virus infection 1991 1993 in ACT, 1995 in WA
Japanese encephalitis virus infection 2001
Kunjn virus infection 2001 Reported as MVE in ACT
Malaria 1991†
Murray Valley encephalitis virus infection 2001
Ross River virus infection 1993
Zoonoses
Anthrax 2001 2002 in SA
Australian bat lyssavirus infection 2001
Brucellosis 1991†
Hydatid infection 1991 No longer nationally notifiable from 2001
Leptospirosis 1991†
Lyssavirus (not elsewhere classified) 2001
Ornithosis 1991 2001 in NSW, Qld did not report 1991, 1997–2001
Q fever 1991†
Tularaemia 2003
Other bacterial diseases
Legionellosis 1991†
Leprosy 1991†
Meningococcal disease (invasive) 1991† Includes conjunctival cases from ACT and NSW
Tuberculosis 1991
Source: NNDSS online (live) data and 2012 NNDSS annual report [3, 6].
Excludes HIV/AIDS and Creutzfeldt–Jakob disease which are notified to other surveillance systems.
ACT, Australian Capital Territory; NSW, New South Wales; NT, Northern Territory; Qld, Queensland; SA, South Australia;
Tas, Tasmania; Vic, Victoria; WA, Western Australia.
* Year became nationally notifiable – listed as 1991 for diseases that were nationally notifiable when NNDSS began in 1991;
diseases introduced after 1991 might have cases notified to NNDSS prior to becoming nationally notifiable.
† Diseases which were consistently notifiable across states for the entire study period.
3266 K. B. Gibney and others
https://doi.org/10.1017/S0950268816001072
Downloaded from https:/www.cambridge.org/core. Kainan University, on 10 Feb 2017 at 06:18:55, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms.