Norms and Standards in Epidemiology:
Case definitions: Measles and Rubella
Rationale for Surveillance
Recommended Case Definitions
Recommended Surveillance Measures
Recommended Minimum Data Elements
Principal Use of Data for Decision-Making
Main Surveillance Indicators
RATIONALE FOR SURVEILLANCE
Measles
Introduction:
In 1994, the Pan American Sanitary conference established the mutual goal
of measles eradication from the Western Hemisphere by the year 2000. Great
progress has been made towards interrupting measles transmission in most countries
of the Americas. However, as of September, 1999, with only 15 months remaining
until the target date for achieving the goal of hemispheric measles eradication,
measles virus continues to circulate in some areas of the Region.
Surveillance:
Measles surveillance is critical for measuring progress towards the goal of
measles eradication in the Americas and for detecting problem areas. Efforts
that are urgently needed to improve the quality of measles surveillance throughout
the Region include:
- All suspected measles cases should be investigated within 48 hours of illness onset, and a serum sample should be collected from the patient upon initial contact with the health provider. This sample must be collected within 30 days of rash onset to be considered adequate;
- To monitor progress toward the achievement of measles eradication, all countries should provide data on a weekly basis to the Region-wide measles eradication surveillance system (MESS)
- Each country should periodically have its measles surveillance system objectively evaluated using the standartized evaluation protocol developped by PAHO. Countries should constantly work to improve the quality of the reporting system;
- Virologic surveillance and molecular epidemiology can provide important information to an eradication program. Appropriate clinical specimens for viral isolation should be obtained from every chain of measles transmission, including all sporadic cases and approximately 5-10 cases from every outbreak. Urine, the most practical specimen to collect for measles virus isolation, should be obtained within 7 days of rash onset and forwarded to a reference laboratory capable of performing measles virus isolation;
- In all countries, measles and rubella surveillance should be integrated.
Rubella
Introduction:
Rubella virus continues to circulate freely in most countries of the region.
After a complete investigation, many suspected measles cases are ultimately
found to be rubella. Moreover, cases of the Congenital Rubella Syndrome
(CRS) have been found in all countries of the Region that have established
CRS surveillance systems. This suggests that CRS is a major public health
problem in all countries of the Americas.
Surveillance:
Rubella surveillance should be integrated with measles surveillance. The
purpose of rubella surveillance is to detect circulation of rubella virus,
not to detect every case of rubella. A separate rubella surveillance system
is not needed. All sera from suspected rubella cases which test negative
for rubella IgM antibodies should be tested for measles IgM antibodies and
vice versa.
RECOMMENDED CASE DEFINITIONS
The measles eradication and rubella control/elimination programs should
use the following standardized case definitions, revised from PAHO's Measles
Eradication Field Guide, 1999, and the WHO Recommended Surveillance Standards
from the 2nd. Ed., June 1999, revised by the PAHO's Communicable Diseases Program.
- Suspected measles case: any patient in whom a health care provider
suspects the possibility of measles.
- Suspected rubella case: any patient in whom a health care provider
suspects the possibility of rubella.
In suspected measles or rubella cases, a serum sample should be collected from the patient upon initial contact with the health provider. This sample must be collected within 30 days of rash onset to be considered adequate.
- Laboratory-confirmed case: a suspected measles or rubella case
that after complete investigation is:
- Confirmed as either measles or rubella using commercially available enzyme immunoassays (EIA) for measles or for rubella IgM antibodies, and/or
- Confirmed by isolation of measles or rubella virus and/or
- Epidemiologically linked to another laboratory-confirmed case (the epidemiological link is established if any contact between the suspected case and the laboratory-confirmed case has occurred anytime during the month prior to rash onset).
-
Clinically-confirmed case: a suspected measles or rubella case that is not completely investigated for any reason. This could include: patients that died before the investigation was complete, patients lost to follow-up, or patients without adequate specimens submitted for laboratory analysis.
-
Discarded: a suspected measles or rubella case that has been completely investigated, including an adequate blood specimen, which lacks serologic evidence of infection, has no virus isolated, and does not have epidemiological link to a laboratory-confirmed case. If laboratory results indicate another viral infection compatible with the clinical symptoms, such as dengue, the case should be discarded as well.
-
Imported Measles Case: a confirmed measles case in a person who traveled to another country with documented measles circulation during the possible exposure period (7-18 days prior to rash onset). The possibility of local exposure must be ruled out through careful investigation.
RECOMMENDED SURVEILLANCE MEASURES
Testing of rubella and dengue suspected cases for measles:
- Blood samples from all rubella suspected cases that are IgM negative for rubella should be tested for measles within 24 hours.
- Blood samples from at least 10% of the dengue suspected cases with rash that are IgM negative for dengue should be regularly tested for measles.
- In the case of laboratory-confirmed rubella or dengue outbreaks, the total number of samples that are negative for either rubella or dengue might be overwhelming. In such a case, the surveillance team, in conjunction with the laboratory, should decide which samples to test for measles.
Investigation and reporting:
- The reporting system must cover health facilities, private practitioners, hospitals and laboratories and have at least one reporting source for every geopolitical unit;
- Written material should be provided to all health personnel describing their responsibilities and how to report cases, collect samples and send them for laboratory confirmation;
- Investigation of all suspected cases should take place within 48 hours
of rash onset. It should include:
- Filling the case report form,
- Investigation of contacts of the suspected case to determine if other cases have occurred,
- Taking blood samples and samples for viral isolation (usually urine) from all sporadic cases and from 5-10 cases from each outbreak.
- Weekly reporting of data, even in the absence of cases, is critical;
- Timely feedback to all participants of the surveillance system, keeping them informed of where and when cases are occurring, is essential;
- The reporting system must be monitored monthly using the surveillance indicators;
- Cooperation from the private medical community by reporting suspected cases to the system is essential for all surveillance efforts.
RECOMMENDED MINIMUM DATA ELEMENTS
Case-based data (to be linked using the unique identifier to
specimen-based data for analysis): (I) unique identifier; (II) geographical
area (district and province); (III) name; date of birth (IV); date of rash
onset (V); date of notification (VI); date of case investigation (VII);
date of specimen collection (VIII); date when specimens were sent to the
laboratory (IX); number of doses of measles-containing vaccine received
(X); (XI) date of last doses of measles-containing vaccine; (XII) if source
of infection was identified; (XIII) results of serology; (XIV) results of
viral isolation; (XV) final classification; (XVI) name of investigator.
See attached Measles-Rubella case report form.
Specimen-based data (to be linked to case-based data for analysis):
(I) unique identifier (MESS number when available); (II) specimen number;
(III) date of rash onset; (IV) date of blood (or urine, nasopharyngeal secretion)
specimen collection; (V) date specimen sent to laboratory; (VI) date specimen
received in laboratory (VII) results of serology; (VIII) results of viral
isolation.
PRINCIPAL USES OF DATA FOR DECISION-MAKING
- Track measles/rubella virus circulation (in an eradication process, one case must be considered as an outbreak;
- Detect and investigate outbreaks to ensure proper case management and determine reasons for its occurrence;
- Efforts should be made to determine sources of measles virus introduction, transmission patterns and specific risk factors for acquiring measles;
- Monitor routine coverage for immunizations in all municipalities and focus efforts in high-risk municipalities (those where vaccination coverage is lower than 95%) for planning mopping up and other immunization activities;
- Identify when next follow-up campaign is due;
- Monitor performance of surveillance using standard indicators and strengthen
surveillance in low performing areas. · Provide evidence for measles-free
certification.
- % of reporting sites that report each week;
- % of reported suspected cases investigated within 48 hours of rash onset;
- % of suspected cases with complete report form;
- % of suspected cases with blood specimen collected within 30 days of rash onset (nonetheless, when outbreaks occur, cases epidemiologically linked to laboratory-confirmed case are confirmed without needing blood specimens);
- % of blood specimens for which results were received within 7 days of receipt of the sample by the laboratory.
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Epidemiological Bulletin, Vol. 20 No. 3, September 1999