MEASLES

Last updated: 03 April 2007

1. Reason for surveillance

• To identify cases and their contacts in order to prevent further spread

• To monitor the epidemiology of measles in NSW and so inform the development of better prevention strategies.

2. Case definition

Suspected case
A suspected case requires:

• clinical evidence (without laboratory or epidemiological evidence)

Probable case
A probable case requires:

• Laboratory suggestive evidence, and

• Clinical evidence.

Laboratory suggestive evidence
Detection of measles specific IgM antibody other than by an approved reference laboratory ² EXCEPT if the case has received a measles-containing vaccine eight days to eight weeks before testing.

Clinical evidence
As with confirmed case.

Epidemiological evidence
Not applicable.

Confirmed case
A confirmed case requires:

• Laboratory definitive evidence, or

• Clinical evidence and epidemiological evidence.

Laboratory evidence
At least one of the following:

• Isolation of the measles virus, or

• Detection of measles virus by NAT, or

• Detection of measles virus antigen, or

• IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to measles virus EXCEPT if the case has received a measles-containing vaccine eight days to eight weeks before testing. (NOTE: paired sera must be tested in parallel), or

• Detection of measles specific IgM antibody confirmed in an approved reference laboratory EXCEPT if the case has received a measles-containing vaccine eight days to eight weeks before testing.

Clinical evidence
An illness characterised by all of the following:

• A generalised maculopapular rash lasting three or more days, and

• Fever (at least 38°C if measured) at the time of rash onset, and

• Cough or coryza or conjunctivitis or Koplik spots.

Epidemiological evidence
An epidemiological link is established when there is contact between two people involving a plausible mode of transmission at a time when:

• One of them is likely to be infectious (approximately 5 days before to 4 days after rash onset); and

• The other has an illness which starts within 7 to 18 (usually 10) days after this contact, and

• At least one case in the chain of epidemiologically linked cases (which may involve many cases) is laboratory confirmed.

Factors to be considered in case identification
Since recent MMR immunisation affects some laboratory tests, the results should be interpreted in the context of the clinical findings. The clinical diagnosis of measles may be confused with other diseases such as rubella, roseola, scarlet fever, human parvovirus infection, enterovirus, adenovirus, HIV, Kawasaki disease and some arboviral infections, so laboratory confirmation for all sporadic cases should be sought.

Testing guidelines

• Public Health Laboratory Network (PHLN) provides information on the laboratory diagnoses of measles. This is available at: www.health.gov.au/internet/wcms/publishing.nsf/content/cda-phln-pubs-measles.htm

• Patients seen within 1 week of onset of rash should have samples collected for direct detection, for culture and clotted blood for serology.

• Patients seen between 1 week and 3 weeks after the onset of rash should have clotted blood collected for serology and a respiratory sample for PCR.

• Patients seen more than 3 weeks after onset of rash should only have clotted blood collected for serology.

• The reliability of serological and direct detection tests for asymptomatic contacts is unknown. Testing of asymptomatic contacts is not recommended.

Measles Serology

• Measles-specific IgM antibody is the mainstay of the diagnosis of acute measles. An IgM response will be present in approximately 75% of patients 3 days after rash onset, rising to approach 100% after 7 days. A measles IgG antibody test should preferably be performed together with the IgM assay to aid interpretation.

• Measles-specific IgM is a sensitive and specific marker of recent measles infection, but can also be detected for 1 to 2 months following immunisation. It is usually present at the onset of the rash, is almost invariably present 4 days after the rash appears and peaks within 10 days.

• A negative result does not rule out a diagnosis of measles if the sample was taken earlier than 72 hours after onset of the rash. A false negative IgM result may also occur in people who have been previously vaccinated against measles. When no measles IgM or IgG antibody is detected in a sample collected within 3 days of rash onset from a case of clinical measles, repeat testing is recommended after 7 days.

• False positive measles IgMs can also occur, and if suspected, the IgM test should be repeated. For sporadic cases, results should be confirmed, ideally by an expert laboratory using the Dade Behring assay.

• Where a false negative or false positive IgM result is suspected, testing for measles specific IgG seroconversion by EIA on paired sera collected 10-14 days apart is helpful.

• Testing paired sera using the complement fixation test (which expresses results in titres) may also be helpful, especially in cases with a history of measles vaccination.

• A 5 mL tube of clotted blood is the preferred specimen for serological testing.

Measles culture and immunofluorescence

• Measles virus may be identified by cell culture from blood, conjunctival swab, throat swab, nasopharyngeal swab or aspirate, or urine if taken before the third day of the rash and urine for up to 10 days after the onset of rash. Antigen testing by immunofluorescence may also be performed on respiratory or urine samples collected during the prodrome or in the first few days after rash onset. Any isolate or immunofluorescence positive material from a NSW laboratory should be referred to the Victorian Infectious Diseases Reference Laboratory (VIDRL) for genotyping.

• Nasopharyngeal aspirates or nasopharyngeal swabs are the preferred sample for antigen detection by immunofluorescence and culture. Throat swabs or nasal washes are suitable for culture but not for immunofluorescence.

Measles PCR

• Respiratory specimens and early catch urine (collected up to 3 weeks after onset of the rash) or sera collected early in the illness can be referred to ICPMR for measles PCR on an urgent basis if necessary (after consultation with the pathologist on call). The Public Health Unit should facilitate communication with and between the laboratories involved concerning collection of suitable specimens and transport arrangements.

• Nasopharyngeal aspirates or nasopharyngeal swabs are the preferred sample for nucleic acid detection by PCR. Throat swabs or nasal washes are also suitable for PCR. A dry sterile swab of the nasal passage combined with a similar swab from the back of the throat is the recommended specimen for detection of viral nucleic acid (PCR). Swabs should be cotton, rayon or dacron-tipped, plastic-coated or aluminium shafted swabs. They should be placed into viral transport medium. Samples should be stored and transported at 4° C. If arrival at the testing laboratory will be delayed more than 72 hours then, if possible samples should be frozen at -70° C and transported on dry ice. Do not freeze at -20° C.

• Early catch urine samples should be stored and transported at 4° C. If arrival at the testing laboratory will be delayed more than 72 hours then, if possible samples should be frozen at -70° C and transported on dry ice. Do not freeze at -20° C. These samples allow epidemiological identification of the measles importation source.

• Heparinised blood for PCR should be stored and transported at room temperature.

¹ Note that the CDNA document Guidelines for the control of measles outbreaks in Australia (July 2000) is no longer current.

The effect of recent vaccination
Vaccine-induced "measles" is a modified form of measles occurring five to ten days after measles vaccination. It is not transmissible and should NOT be classified as measles.

Serologically-diagnosed cases who received a measles-containing vaccine 8 days to 8 weeks before testing may be classified as confirmed measles ONLY if they are also epidemiologically linked to a confirmed case.

²In NSW, serology from laboratories using the Dade Behring kit is acceptable to confirm diagnosis

3. Notification criteria and procedure

Measles is to be notified by:

• Medical practitioners and hospital CEOs on diagnosis (reporting by telephone within 1 hour of diagnosis)

• Laboratories on confirmation (reporting by telephone within 1 hour of diagnosis)

• School principals and directors of child care facilities (reporting by telephone within 1 hour of notification by parent or carer).

Only probable and confirmed cases should be entered onto NDD. Cases that are subsequently shown not to be measles should be removed from NDD.

³ Note, the Dade Behring EIA is thought to be the most reliable commercial test available for measles IgM antibodies and alone provides laboratory definitive evidence of infection (in the absence of recent immunisation).

4. The disease

Infectious agents
The measles virus, a member of the genus Morbillivirus (paramyxovirus).

Mode of transmission
Measles is transmitted by airborne droplets and direct contact with discharges from respiratory mucous membranes of infected persons and less commonly by articles freshly soiled with nose and throat secretions. It is highly infectious.

Timeline
The incubation period is variable, about 10 days (varying from 7 to 18) to the onset of fever and about 14 days to the onset of the rash.

Infectious period
A rule of thumb is that measles is infectious 5 days before, to 4 days after, the appearance of the rash. However in cases with a clear history of time of onset of prodromal illness, the infectious period should be considered commencing 24 hours prior to the onset of prodromal symptoms.

Clinical presentation
The disease is characterised by a prodrome that usually lasts 2 to 4 days and includes fever followed by conjunctivitis, coryza and cough. Koplik spots may be present on the buccal mucosa. A characteristic maculopapular rash appears about 2 to 7 days after the onset of the prodrome, and begins on the face or upper neck, spreads to become generalised and lasts 4 to 7 days. The rash is not itchy. Cases are usually pretty miserable, and complications such as middle ear infection, bronchopneumonia and encephalitis can follow. Infection in pregnancy can be severe for the woman and can result in increased risk of premature labour or spontaneous abortion. Although there is no association with congenital abnormalities, congenital measles infection can occur if the infection is contracted late in pregnancy. Prophylaxis and specialist care are required in these cases.

5. Routine case investigation

Response times
Investigation
On same day of notification of a suspected, probable or confirmed case:

• Begin follow-up investigation using the Measles Investigation Form.

• Notify the Communicable Diseases Branch of the case's age, sex, date of onset, vaccination history, laboratory status, likely source of infection, other people at risk of infection and follow up action taken.

Data entry
Enter confirmed and probable (but not suspected) cases on NDD within 1 working day of notification. The date of onset is the onset of illness, not of the rash.

Enter information on viral typing (if done) on NDD within 3 working days of receipt of results.

Cases subsequently shown not to have measles should be removed from NDD within 1 working day.

Response procedure
The response to a notification will normally be carried out in collaboration with the case's health carers. Regardless of who does the follow-up, PHU staff should ensure that action has been taken to:

• Seek the doctor's permission to contact the case or the relevant care-giver

• Find out what the case or relevant care-giver has been told what the diagnosis is before beginning the interview.

• Review case and contact management

• Confirm the onset date and symptoms of the illness

• Confirm results of relevant pathology tests, or recommend that the tests be done. The choice of tests depends on the time since rash onset (see testing guidelines, above). In an established outbreak confirmatory laboratory tests are not required in cases with classical presentation and a clear epidemiological link.

• Collect specimens for culture and PCR on ≥1 case within a cluster and ≥2 cases in an outbreak. Check with ICPMR first, but this usually requires:

• Ensure that laboratories send copies of these results to the Public Health Unit.

• Consider the value of measles genotyping in the setting of a measles outbreak (using specimens from culture or PCR).

Case management
Treatment
Supportive only.

Education
The case or relevant caregiver should be informed about the nature of the infection and the mode of transmission. By the time the case of measles is identified and notified, the case may already have transmitted the virus to other susceptible people. The case should be advised to stay at home in isolation while infectious and to avoid contact with susceptible people (see below), pregnant women and immunosuppressed people.

Isolation and restriction
Exclude cases from school, preschool or childcare and advise to stay in isolation (and specifically advise against interaction with susceptible people) until 4 days after the onset of the rash.

When measles is suspected, hospitalised cases should be kept in strict respiratory isolation (and preferably in a negative pressure room) until 4 days after the onset of the rash. Only healthcare workers who are immune should care for these patients.

When a case is isolated at home he or she should not mix with people who may be susceptible and who have not already been exposed. For example, the household should not have visitors while the case is infectious.

Environmental evaluation
None usually required.

Contact management
Identification of contacts
Since measles is transmitted by airborne means, anyone who has shared the same air as the case for any length of time while infectious can be defined as a contact. In general, contacts may be prioritised in the following order, although it will not always be feasible for the public health unit to identify individuals and arrange prophylaxis for them. In unclear or unusual situations, contact management should be discussed with Communicable Diseases Branch. Contacts include (in priority order for prophylaxis):

• All household members

• All people sleeping overnight in the same room as the case (for example, in a hospital, boarding school or military barracks)

• All children and adults at family day care, childcare, preschool, school or other educational setting who share a classroom with the case

• People who stayed in a waiting area at the same time as the case (for example, patients in a health care facility's waiting room and any people accompanying these patients) and people who waited in the waiting area or who were seen in the same consultation room up to 2 hours after the infectious case left.

• All work colleagues of the case who share the same work area

• Others who attend or work in the same educational institution as the case, and may have spent time in the vicinity of the case, but do not share a classroom (for example, a high school, college, lecture theatre block).

• Passengers on an aeroplane who were seated in the same row and two rows in front of and behind an infectious case.

• For others who cannot be individually identified but who may have been present in the general area where the cases was known to be (for example, cinemas, shopping centres, aeroplane flights and restaurants) consideration should be given to the need to provide notices, or media informing them of their possible exposure.

A person considered susceptible to measles is someone who cannot provide acceptable presumptive evidence of immunity to measles. A person can be considered to have acceptable presumptive evidence of immunity to measles if they meet one of the following criteria:

• Children aged 1 to 4 years who have documented evidence of having received one dose of a measles-containing vaccine

• Persons over 4 years of age and born during or since 1966 who have documented evidence of receiving 2 doses of a measles-containing vaccine (unless serological evidence indicates otherwise)

• Persons born before 1966 (unless serological evidence indicates otherwise)

• Documented evidence of immunity

• Documented evidence of laboratory confirmed measles.

Prophylaxis
Susceptible contacts should be provided with preventative therapy (either normal human immunoglobulin or MMR vaccine) according to:

• time elapsed since exposure to an infectious case. Where there has been ongoing exposure (such as with household contacts) the time since exposure should be calculated from the first contact during the infectious period;

• age;

• previous MMR immunisation history; and

• current immunosuppression or pregnancy.

Tables 1 and 2 are provided in the appendix for this purpose.

NHIG is available through the Australian Red Cross Blood Service (ARCBS) during working hours by calling the Transfusion Medical Officer on 9229-4347, or the After Hours Medical Officer on call 9229 4444. ARCBS keeps a small stock of NHIG at its Clarence Street, Sydney and Newcastle Distribution Departments. These departments are not set up for public access. For individual doses, the ARCBS may provide NHIG from stock at a local hospital, issue stock direct or supply it via CSL, depending on the urgency.

For outbreaks, the PHU should discuss with ARCBS the number of potential patients involved and the best way to distribute the product according to whether a clinic will be set up or whether patients will be referred to individual GPs. If a clinic is planned, ARCBS will arrange for product to be transported to the site of clinic, but the PHU will need to ensure availability of suitable storage for the NHIG (e.g., the hospital blood bank or pharmacy). If it is planned to refer patients to individual GPs, a suitable central access point for NHIG will need to be identified (e.g., a local hospital blood bank or pharmacy). The PHU is responsible for notifying GPs on the process for accessing NHIG for their patients.

Small stocks of NHIG may be held at some hospitals including: Westmead, Wollongong, Gosford, John Hunter, Cessnock, Albury, Orange, Macksville, Port Macquarie, Lismore, Tamworth, Armidale, Narrabri, Wagga Wagga, Tumut, Griffith, Broken Hill, Hornsby and Sutherland.

MMR vaccine should be delayed for 3 months after administration of NHIG.

Education
Advise susceptible contacts (or parents/guardians) of the risk of infection and counsel them to watch for signs or symptoms beginning 7 to 18 days after the first contact with an infectious case (or longer if the contact received immunoglobulin). They should avoid contact with other susceptible people, pregnant women and immuno-compromised people during this period. If thought to be infectious, they should also be advised to avoid doctors' waiting rooms.

Advise the case's doctor that all people who used the same waiting room area or consultation room up to two hours following the case's departure require immediate assessment and prophylaxis if susceptible.

A sample script and measles: information for contacts factsheet can be found in the appendix.

Isolation and restriction
Children who were enrolled in primary school, preschool or child care should be excluded as follows:

• Unvaccinated contacts should be excluded until 14 days after the onset of the rash in the last case occurring at the facility. However they may return if vaccinated within 72 hours of first exposure to an infectious case or if they receive NHIG within 7 days of exposure.

• Immunocompromised children or staff should be excluded (regardless of their measles vaccination status) until 14 days after the onset of the rash in the last case occurring at the facility. Exclusion is advised for their own safety even if they receive NHIG

• Immunisation records are unlikely to be available for high school children and those enrolled before 1994 cannot be involuntarily excluded under the Public Health Act. Susceptible contacts in high school should be advised to stay away until 14 days after the onset of the rash in the case. They may return if vaccinated within 72 hours of first contact with an infectious case or if they receive NHIG within 7 days of exposure.

6. Managing special situations

Since the transmission of measles frequently occurs before diagnosis, the spread of the disease can be facilitated wherever susceptible individuals gather in groups.

Cases among children or staff at school or in child care
In addition to routine case and contact management, ask about possible cases occurring among attendees or employees within the previous 18 days. Daily surveillance to detect possible cases may be needed and should be considered for 18 days after the last infectious case attended. All suspected cases should be investigated and measures taken to minimise or eliminate secondary transmission from these cases.

Parents and staff should be provided with information about the disease and its prevention. Written information such as a fact sheet is recommended, but an information meeting for parents may also be useful (see appendix for sample letters to parents). Vaccination of all susceptible contacts should be recommended. Consider holding an immunisation clinic at the facility.

Cases among health care workers or patients in a health care facility
Refer to policy directive: Occupational Assessment, Screening & Vaccination Against Specified Infectious Diseases PD2007_006

For suspected, probable or confirmed cases among health care workers or patients in a health care facility, consult immediately with staff from infection control or staff health to institute a management plan appropriate to the facility. This should include procedures for:

• Defining and identifying contacts

• Informing contacts and organising management where appropriate

• Keeping infectious patients in respiratory isolation for 4 days after the appearance of the rash, and ensuring that susceptible individuals do not enter any room for 2 hours after an infectious case has used it. Susceptible people entering this room within the two hour period should be considered direct contacts

• Ensuring that only staff who are immune (see section 5) provide direct care to infectious patients

• Vaccinating susceptible contacts among patients and staff who have not received 2 doses of a measles-containing vaccine. Susceptible patients who are not vaccinated within 72 hours or do not receive NHIG within 7 days of first exposure, should be isolated and discharged from hospital as soon as possible. Susceptible staff who are not vaccinated within 72 hours or receive NHIG within 7 days of first exposure should be redeployed to duties not requiring direct patient care (for up to 14 days after onset of the rash in the last case occurring at the facility while the staff member was susceptible)

• Carrying out active surveillance for measles, where practical, among exposed: inpatients, inpatients discharged before the diagnosis of the first case, staff, students, volunteers and visitors

• Investigating staff members presenting with prodromal symptoms and ensuring that the affected person stays away from work until 4 days have elapsed after the onset of the rash, (or a measles diagnosis is excluded)

• Reviewing staff health records to ensure that all have been protected in line with current recommendations.

Appendices

• Measles Investigation Form  http://www.health.nsw.gov.au/infect/pdf/measles_form.pdf
• Post Exposure Prophylaxis Table for Exposures  http://www.health.nsw.gov.au/infect/pdf/measles.pdf#page=7
• Factsheet "Measles: Information for contacts"  http://www.health.nsw.gov.au/infect/pdf/measles_contact_factsheet.pdf
• Sample letter - primaryschool, preschool and childcare exclusion  http://www.health.nsw.gov.au/infect/pdf/measles.pdf#page=9
• Sample letter - information for vaccinated primary school, preschool and childcare contacts  http://www.health.nsw.gov.au/infect/pdf/measles.pdf#page=10