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It has been a long road to the control of measles in Australia. Live
attenuated measles vaccine was licensed in 1968, and included in
childhood vaccination schedules in 1971. Even after the first
national measles campaign, in 1988, coverage remained too low
(85%)1 to achieve herd immunity, as
evidenced by major measles outbreaks in many areas in 1993-1994. In
1994, a second dose of measles-mumps-rubella (MMR) vaccine was
introduced for all children aged 10-16 years. Although the incidence
of measles declined, seroprevalence studies2 indicated that further
measles outbreaks were likely.
In response to these findings, the Australian Measles Control
Campaign (MCC) was launched in July 1998. The centrepiece of this
campaign was administration of a dose of MMR vaccine to all primary
school children in the second half of 1998. This "catch-up" dose was
needed before lowering the recommended age for the second dose of MMR
vaccine to four years in 1999. After the MCC, an estimated 96% of
children aged five to 12 years had received two doses of MMR
vaccine.3 As a result of this campaign
and the continuing efforts to eradicate measles, it is hoped that
Australia will soon be shown to have joined other countries, such as
the United States,4 the United
Kingdom5 and Finland,6 where
indigenous measles transmission has been interrupted.
The better the control of measles, the lower the probability that
someone presenting with fever and rash will have measles, and the
poorer the positive predictive value (PPV) of a clinical diagnosis.
Even in 1990-1993, before any major measles control measures, a study
of 58 people notified with measles in eastern Sydney found that only
49% of cases were serologically confirmed.7 A case definition of
morbilliform rash, cough and fever at rash onset had a PPV of
69%.7
In this issue of the Journal, there is a report of a
larger study of enhanced measles surveillance in Victoria from July
1997 to December 1998 (ie, primarily conducted before the MCC) which
showed a much lower level of confirmation.8 Only 8% of the 248 notified
cases that could be classified on the basis of serological results
were confirmed as measles. The PPV of the National Health and Medical
Research Council (NHMRC) clinical case definition for considering
public health action9 was as low as 5% when
secondary cases from clusters were excluded.8 Since the MCC, the
proportion of serologically confirmed cases is likely to have fallen
even further. In the UK, after a similar school-based MMR program in
1994,5 and in Finland 12 years after
high coverage with a two-dose MMR schedule,6 only about 1% of suspected
cases were shown to be measles.
These developments necessitate major changes in the approach of
medical practitioners to suspected measles, especially in
general practice where most cases will be seen. The latest draft of the
revised NHMRC guidelines for measles control emphasise that
confirmation by detection of measles IgM in a serum specimen is
essential when measles is clinically suspected.10 This policy is
also recommended by the authors of the Victorian study and by the
National Measles Surveillance Strategy.11 Confirmation is
particularly important in sporadic cases, where the prior
probability of measles is especially low, and should also be obtained
from at least two cases during an outbreak. The high level of
laboratory testing achieved in Victoria is encouraging. However,
overall, only 44% of the 428 cases accepted as measles notifications
in Australia between January 1998 and June 1999 were laboratory
confirmed (personal communications from State and Territory health
departments). It may be possible to improve this percentage --
although teams of venepuncturists are impractical for many areas of
Australia, arrangements to bleed patients can usually be made in
consultation with local public health authorities.
Considerable interest has also focused on non-invasive diagnostic
methods, such as salivary testing. This method has been used in the UK
but has technical difficulties,11 making timely testing
more difficult than for serological testing. Even when serological
testing is done, as measles becomes rare the likelihood of a falsely
positive measles IgM will rise, as found in Victoria and
elsewhere.4 A positive measles IgM test
should therefore be confirmed by a reference laboratory, especially
in sporadic cases.
Clinicians should be aware that many viral infections in children may
resemble measles clinically, and that measles is more likely in older
children and young adults than in infants. After control of measles in
Finland,6 37% of 993 children with
suspected measles had serological evidence of infection caused by
parvovirus, enteroviruses, adenovirus or human herpesvirus type 6
(HHV-6).12 The most common
serological diagnoses were parvovirus infection, in children aged
four to 15 years, and enterovirus and HHV-6 infection, in children
aged under four years. In Sydney, in 1990-1993, the mean age of
patients with confirmed measles was 11.3 years,7 and, in Victoria
in 1997-1998, more than half (53%) the patients with confirmed
measles were aged at least 10 years.8 An outbreak of measles in
Victoria in 1999, after the MCC, indicates the likely future pattern
of measles in Australia -- 84% of patients were aged 18-30 years and all
patients aged one to eight years were unvaccinated.13
Sustained measles control will require further efforts in young
adults as well as continued high coverage with two doses of measles
vaccine in children. Young adults, especially those attending
tertiary institutions or planning travel to areas where measles
remains endemic, should be encouraged to have a second dose of MMR or
serological confirmation of measles immunity.
Peter B McIntyre
Deputy Director
Heather F Gidding
Epidemiologist
National Centre for Immunisation Research and Surveillance of
Vaccine
Preventable Diseases, Royal Alexandra Hospital for
Children
and University of Sydney, Sydney, NSW
Gwendolyn L Gilbert
Director, Centre for Infectious Diseases and Microbiology
and
University of Sydney, Sydney, NSW
- Australian Bureau of Statistics. National health survey.
Children's immunisation, Australia, 1989-90. Canberra: ABS, 1992.
(Catalogue no. 4379.0.)
-
Gilbert GL, Chan S-W, Escott R, et al. Seroepidemiology of measles
in New South Wales, 1997. Report to the National Centre for Disease
Control, Commonwealth Department of Health and Aged Care, 1998
(available from the Department).
-
National Centre for Immunisation Research and Surveillance of
Vaccine Preventable Diseases. Australian measles control campaign
1998. Evaluation report. Sydney: University of Sydney, Royal
Alexandra Hospital for Children, 1999.
-
Watson JC, Redd SC, Rhodes PH, Hadler SC. The interruption of
transmission of indigenous measles in the United States during 1993.
Pediatr Infect Dis J 1998; 17: 363-366.
-
Gay N, Ramsay M, Cohen B, et al. The epidemiology of measles in
England and Wales since the 1994 vaccination campaign. Commun Dis
Rep CDR Rev 1997; 7: R17-R21.
-
Peltola H, Hienonen OP, Valle M, et al. The elimination of
indigenous measles, mumps, and rubella from Finland by a 12-year,
two-dose vaccination program. N Engl J Med 1994; 331:
1397-1402.
-
Ferson MJ, Young LC, Robertson PW, Whybin LR. Difficulties in
clinical diagnosis of measles: proposal for modified clinical case
definition. Med J Aust 1995; 163: 364-366.
-
Lambert SB, Kelly HA, Andrews RM, et al. Enhanced measles
surveillance during an interepidemic period in Victoria. Med J
Aust 2000; 172: 114-118.
-
National Health and Medical Research Council. Measles:
guidelines for the control of outbreaks in Australia. Canberra:
NHMRC, 1996.
-
National Health and Medical Research Council. Measles:
guidelines for the control of outbreaks in Australia [draft].
Canberra: NHMRC, 2000.
-
Heath T, Burgess M, McIntyre P, Catton M. The national measles
surveillance strategy. Commun Dis Intell 1999; 23: 41-49.
-
Davidkin I, Valle M, Peltola H, et al. Etiology of measles and
rubella-like illness in measles, mumps, and rubella-vaccinated
children. J Infect Dis 1998; 178: 1567-1570.
-
Lambert S, Lynch P, Morgan M, Gercovich D. Measles outbreak --
young adults at high risk. Victorian Infect Dis Bull 1999; 2:
21-22.
©MJA 2000
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