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Enhanced measles surveillance during an interepidemic period in Victoria
S B Lambert1, H A Kelly, R M Andrews
1Victorian Infectious Diseases Reference Laboratory, Melbourne.
Objective:
To describe results of the first two years of enhanced measles surveillance in Victoria.
Design:
Case series identified through enhanced measles surveillance.
Participants And Setting:
All measles cases notified to the Disease Control Section, Department of Human Services, Victoria, in 1997 and 1998.
Main Outcome Measures:
Proportion of notified cases laboratory confirmed as measles, rubella, or human parvovirus infection; identification of clusters (two or more linked cases of measles); and utility of the National Health and Medical Research Council clinical case definition for suspected measles.
Results:
Rates of laboratory testing of notified cases improved after introduction of a paediatric phlebotomy service in July 1997, from 21 of 90 notified patients (23%) in the preceding six months, to 258 of 317 notified patients (81%) between July 1997 and December 1998. Of the 317, only 19 (6%) were laboratory confirmed with measles, while a further 26 (8%) were laboratory confirmed with human parvovirus infection (18) or rubella (8). Three clusters of measles, involving 11 cases, were identified during 1998. Use of the NHMRC case definition did not greatly improve the positive predictive value for diagnosis of measles above that of notification alone (14% versus 8%).
Conclusions:
Circulation of measles virus in Victoria in 1997 and 1998 appeared minimal. In this interepidemic period most notified cases of measles were not measles; to identify true cases, surveillance during an interepidemic period must include laboratory testing of notified cases.