Background |
Measles control is defined as a significant reduction in measles incidence and mortality. When high levels of vaccine coverage are attained (75-80 %), measles incidence decreases and the intervals between outbreaks are lengthened (4-8 years) as compared to those observed during the pre-vaccine era (2-4 years).
Measles-elimination is defined as:
- - Prevention of periodic measles outbreaks (by timely immunization of susceptible individuals in high-risk areas and by improving overall population coverage level)
- - Elimination of indigenous transmission of measles virus
- - Maintenance of the susceptible population below a certain critical number required to sustain transmission of the virus.
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Measles surveillance objectives |
During the measles control phase, the objectives of measles surveillance are:
- - Monitoring of incidence and coverage in order to assess progress
- - Identification of high risk areas and populations where immunization and surveillance services must be improved
- - Understanding the changing epidemiology of the diseases
- - Predicting the occurrence of outbreaks
- - Detecting and investigating outbreaks.
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During the measles elimination phase and once measles become rare, specific objectives of measles surveillance are added:
- - Immediate detection of any suspected cases
- - Confirmation by laboratory diagnosis
- - Focusing on the areas where measles virus is circulating or may circulate
- - Identification of possible sources of infection.
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Measles case definition |
- Suspected cases of Measles
- - A suspected case of measles is any maculo-papular rash with fever.
- - Or a suspected case of measles is any case diagnosed by the physician as measles.
- Confirmed cases of Measles: A confirmed case of measles is the case with positive IgM measles serology.
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Measles reporting |
Three operational channels for measles reporting are used for:
- - Immediate passive reporting
- - Hospital weekly zero reporting
- - Hospital active surveillance
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Measles investigation |
Measles investigation aims at collecting data and specimens from cases, in order to confirm cases and explain the occurrence of the case by evaluating the reported vaccination status and source of infection.
- Data collection: Data is collected through a specific form for measles and rubella investigation. The practitioner who reported the case is asked to fill the specific form and send it to the Epidemiological Surveillance Program (ESP). Collected data is related to:
- - Demographic characteristics: address, age, gender
- - Clinical findings: rash and rash onset, fever lymph-adenopathies ...
- - Complication issues: hospitalization, pneumonia, gastro-enteritis and death
- - Vaccination status: for measles and rubella containing vaccines
- Specimen collection and laboratory confirmation: The patient (or his family) and the practitioner are asked to provide clinical specimen (blood, dried blood or oral fluid) from the case during the 28 days following rash onset. During the acute measles case, specific antibodies increase rapidly and are detectable from day 4 to day 28.
Collected clinical specimens are sent to the Rafic Hariri University Hospital laboratory (RHUH), which is designated as the current national reference laboratory.
At RHUH, specimens are tested for Measles IgM using ELISA method. If Measles IgM serology is negative, specimens are tested for Rubella IgM.
Results are communicated to the ESP, who has to communicate them to the physician. |
Measles classification |
The WHO-laboratory classification is used as follows:
- - Measles laboratory-confirmed: a case that meets the clinical case definition and is laboratory confirmed (i.e. presence of measles-specific IgM antibodies)
- - Measles epidemiologically-confirmed: a case that meets the clinical case definition and is linked epidemiologically to a laboratory-confirmed case (i.e. direct contact to a laboratory-confirmed case in which rash onset occurred 7-18 days earlier)
- - Measles clinically-confirmed: a case that meets the clinical case definition and for which no adequate blood specimen was taken.
- - Measles-discarded: a suspected case that does not meet the clinical or laboratory definition.
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