What is the best course of action when there is a measles epidemic in a nearby municipality?

The response to the outbreak needs to be developed fast and aggressively. The type of outbreak response varies, depending on a number of factors, including the level of susceptibility in the population, risk for spread and complications, and the existing health-service infrastructure.

In order to enhance the capacity to respond to measles outbreaks, a district level Outbreak Coordination Committee or any equivalent sub-national level multidisciplinary group should be created prior to the occurrence of outbreaks. The committee should be chaired by a government official, if available, and should include all potential partners (including NGOs working in the affected area) (see Annex 2). The role of the committee is to coordinate the outbreak risk assessment, and implementation and evaluation of the response.

The Outbreak Coordinating Committee should ensure that the following actions are carried out:

1. laboratory confirmation of the outbreak;

2. ensuring adequate clinical management of cases;

3. intensifying surveillance and notification of suspected cases;

4. assessing the risk of a large outbreak with high morbidity and mortality;

5. investigating a confirmed measles outbreak;

6. implementing control and preventive measures (including vaccination activities);

7. ensuring effective community involvement and public awareness.

It should be noted that the order of these actions (a to g above) is not intended to indicate a chronological order for their implementation. Many of these actions should be undertaken concurrently as soon as the outbreak is suspected or confirmed.

Figure 1 is a flow chart summarizing the actions that should be taken when a measles outbreak is suspected or confirmed. Next to each action item, there is a reference to the section of the document addressing the action item.

Figure 1

A flow chart summarizing the actions that should be taken when a measles outbreak is suspected or confirmed.

A. Laboratory confirmation of a measles outbreak

When an outbreak of measles is suspected it is critical to rapidly determine if the suspected outbreak is indeed a real outbreak by verifying that the reported suspected cases comply with the recommended clinical case definition, and that the increase in the number of reported cases meets the definition of an outbreak (see Part II). Whenever possible, all suspected measles outbreaks should be confirmed by the laboratory to be due to measles virus infection. In this, blood should be drawn from the first 5–10 suspected cases within an affected geographical area, for laboratory confirmation (the presence of measles-specific IgM antibodies) of the outbreak in that area. If there is suspicion that the outbreak has spread to an adjacent area, 5–10 blood specimens should also be collected from suspected cases in these areas, unless there is clear epidemiologic linkage between the two areas/districts. Once a measles outbreak is laboratory-confirmed, it is not necessary to collect specimens from every suspected case. Additional cases can be confirmed if they meet the clinical case definition and are epidemiologically linked to a laboratory-confirmed case.

For virus detection and sequence information, oropharyngeal swab specimens should be collected from five cases within the first seven days of rash onset from each outbreak. Sequence information can assist national control programmes, determine transmission pathways, and define geographical distribution of measles virus genotypes.

There is no need to incur delays while waiting for laboratory confirmation; response activities should be initiated as soon as there is a suspected outbreak (see definitions in Part II).

As mentioned in Part II above, if laboratory confirmation is not possible, an outbreak may be documented through a sustained and progressive rise in clinically-confirmed cases over a three-week period.

See Annex 1: Laboratory procedures

B. Ensuring adequate clinical case management

Significant morbidity and mortality are associated with measles. During an outbreak, adequate case management is critical in reducing measles mortality. There is currently no specific treatment for measles infection. Administration of vitamin A to children with measles has been shown to decrease both the severity of disease and the case-fatality rate, and WHO recommends that vitamin A be administered to all children with acute measles. One dose (50 000 IU for infants aged less than six months, 100 000 IU for infants aged 6–11 months, and 200 000 IU for children aged ≥ 12 months) should be administered on the day of measles diagnosis, and one dose should be administered the following day. Supportive treatment should be provided for all cases, including additional fluids (such as oral rehydration solution) and antipyretics. Antibiotics should be used for cases complicated by otitis media or pneumonia, and nutritional therapy is indicated for children with malnutrition. Many children require four to eight weeks to fully recover their pre-measles nutritional status.

According to the existing Integrated Management of Childhood Illnesses (IMCI) guidelines, prophylactic use of antibiotics is not recommended for uncomplicated cases. However, a recent study of measles cases in an impoverished community found prophylactic use of antibiotics was associated with improved outcomes (23). Detailed guidance on measles clinical case management is available in the WHO protocol for IMCI for treating measles complications (http://www.who.int/child-adolescent-health/integr.htm) and management of the child with a serious infection or severe malnutrition (24).

C. Intensifying surveillance and notification

1. Intensify surveillance

When an outbreak is suspected, surveillance should be intensified to ascertain the size and the geographical extent of the outbreak. As mentioned in Part II, whenever possible, all outbreaks should be laboratory-confirmed and, as already described, appropriate specimens should be taken from suspected cases.

Health staff at the health facility or district level should be vigilant and investigate any reports or rumors of measles cases occurring in the community, or when there is an epidemic occurring in a neighbouring area. Such investigations should either confirm (or reject) the existence of measles virus circulation.

At the health-facility level, measles surveillance should be intensified to actively seek additional cases. In this case, the following steps should be taken:

1. Investigate and collect data from each suspected case, adding the data to the line-listing form (see Annex 4). Data collected should at minimum include (name, address, age, sex, date of rash onset, vaccination status, date of last vaccination and, if applicable, date of specimen collection).

2. Institute weekly reporting, regardless of frequency of reporting prior to the outbreak.

3. If possible, conduct regular calls or visits to schools, hospital emergency rooms and other health facilities, plus selected paediatricians for case finding, especially in urban areas.

4. If time and resources permit, additional case finding should be conducted starting in health facilities where cases have already been reported, and including a search for cases in the community as follows:

   1. search for additional cases in the registers;

   2. look for patients who may have presented with similar signs and symptoms as measles;

   3. request health staff to search for similar cases in registers of neighbouring health facilities;

   4. ensure that private hospitals and clinics are included in the search;

   5. conduct house-to-house visits in affected areas.

Districts should aggregate data on measles cases and deaths (at minimum by age group, vaccination status and date of rash onset) and send weekly reports to the next (higher) administrative level, e.g. the Province (see also WHO Regional Office for Africa guidelines for measles surveillance (25).

2. Notify the authorities

Once an outbreak has been laboratory-confirmed, block and district staff must immediately notify the next administrative level, e.g. the district (in case of block) or the Province (in the case of a district). The immediate notification report should include information on the number of cases and deaths by age group, vaccination status and date of rash onset, the geographical location of the outbreak and the activities planned to investigate and manage the outbreak. In addition, any supplies needed and technical support should be sought at this time (see section below).

Health authorities and health facilities at all levels and in nearby jurisdictions should be notified of the outbreak and updated as frequently as possible. This will allow them to be on the look-out for increases in the number of suspected measles cases and to begin appropriate preventive actions in their areas. If an importation from another country or Province may have occurred, the local health officials in the country or Province from which it was imported should be notified, and given all the information available. If a case has traveled or has had close contact with individuals from other areas of the country either during his/her exposure period (6–18 days before rash onset) or infectious period (i.e. from four days before to four days after rash onset), the surveillance coordinator in those areas should be notified immediately to alert them to the risk of measles outbreak in their areas.

Under the International Health Regulations (IHR) (2005), measles outbreaks could, under certain circumstances, be considered as Public Health Emergencies of International Concern (PHEIC). All measles outbreaks should be reported to the health authorities at the local, regional and national levels. At the national level, the decision instrument for the assessment and notification of events that may constitute PHEIC (outlined in Annex 2 of the IHR 2005, reference 5) should be used to determine if the measles outbreak should be notified to WHO. If so, the outbreak should be notified through the national IHR focal point.

D. Assessing the risk of a large outbreak with high morbidity and mortality

As soon as the outbreak is suspected, the risk of a large outbreak with high morbidity and mortality must be assessed. This assessment is needed to determine what type of vaccination response is most appropriate to control the outbreak. For this, the following evaluations should be carried out.

1. Evaluate the susceptibility of the population and potential for spread both in the affected and neighbouring areas

Approximately 15% of children vaccinated at nine months of age and 5%–10% of those vaccinated at 12 months of age fail to seroconvert, and are thus not protected after vaccination. The example of district X with a population of 500 000 and 12 500 births per year illustrates the build up in susceptibles. If 80% of children aged nine months receive measles vaccination through routine health services, and assuming 85% vaccine effectiveness, only 8500 children (12 500 × 0.8 × 0.85, or 68%) in each birth cohort of 12 500 will be protected against measles, and 4000 children (32%) will remain susceptible to measles. Thus, 4000 children will be added each year to the pool of measles-susceptible children. As a general guide, an outbreak is likely to occur when the pool of susceptible children reaches the size of one birth cohort. In this example, an outbreak is likely to occur in district X after 3–4 years (see Table 2). It should be noted that this method only provides an approximation of the susceptibles in a population (i.e., those arising from new births) as it does not take into account other sources of susceptibles in the population. For example, the susceptibles in the population in the age beyond the target age group, or susceptibles migrating into the population are not included.

Table 2

Table showing an approximation of the buildup of susceptible children with each successive birth cohort over a four-year period in the example of district X above.

To estimate the susceptibility profile by age group, the proportion of susceptible persons should be calculated by taking into account the estimated population and the vaccination coverage of each age group from six months to 14 years and 11 months of age (through both routine immunization and campaigns) and estimated vaccine efficacy.

2. Evaluate the risk of further transmission, morbidity and mortality. For this, the following factors should be taken into account

• Population characteristics such as size, density, movement, and setting (e.g. community spread throughout a district, or limited spread within a subpopulation; resource poor settings).

• Under five mortality rates.

• Nutritional, including vitamin A, status.

• HIV prevalence in the population.

• Period of the year (considering potential for seasonal outbreak) and plans for any festivals or other social events that will result in increased opportunities for spread.

• Number of cases reported and comparison with data from previous years.

• Access to health services.

E. Investigating a confirmed measles outbreak

1. Collect data

During an outbreak, data collection should be limited to obtaining basic information from each case (name, address, age, sex, immunization status, date of last vaccination, symptoms, date of rash onset, date of specimen collection, outcome), which should then be added to the line-listing. Any additional information on the population where the outbreak occurs that may shed light on the presence of risk factors for measles infection should, if possible, be obtained (e.g. available information on the HIV prevalence or nutritional status of the population). The data should be analysed rapidly to determine the extent and severity of the outbreak, vaccine effectiveness, potential risk factors for measles infection, and possible causes of the outbreak (e.g. vaccine failure or failure to vaccinate).

2. Describe the outbreak

Describe the outbreak in terms of time, person, and place.

• Time: What are the dates of rash onset among cases? Allows the creation of the epidemic curve.

• Person: What are the characteristics of the cases (e.g. age distribution, vaccination status)?

• Place: Where do cases live? Where are the most affected areas/localities? Allows the mapping of the geographical extent of the outbreak (e.g. spot map or table with attack rates by district).

Details and examples of methods defining the extent of the outbreak can be found in the WHO Module on best practices for measles surveillance (6).

3. Analyse data

Data collected should be analysed by district-level staff to gain a better understanding of the outbreak and use the information to guide the outbreak response activities. Below are important indicators that provide information on the severity of the outbreak. For information on how these are calculated see Annex 3.

Attack rate (AR)

The AR expresses the number of cases among the total population in a given area during a defined period of the outbreak. If population data by age group are available for the area affected by the outbreak, age-specific attack rates can be calculated. Age-specific attack rates help to identify the age ranges for priority vaccination. AR allow for comparison of the extent of the outbreak between different populations (e.g. by age group or by geographical location). For example, Table 3 shows the attack rates by commune (districts within the city) in Niamey in the Republic of the Niger for the epidemic in 2003–2004.

Table 3

Attack rates for measles by commune of origin of patients, Niamey, Niger (1 November 2003 – 6 June 2004).

It should be emphasized that it is important to determine the place where the suspected case was infected rather than the place from where he/she may seek care, as patients may seek health care in a different area to where they live. This information helps to follow the geographical spread of the epidemic and identify areas at higher risk. Ideally, it is also important to determine the attack rate by age group.

Weekly incidence

Weekly incidence is the number of new cases of the disease by week in a specified population. Attack rates and weekly incidence numbers permit comparison between different geographical areas and monitor the progression of the outbreak over time.

Case-fatality ratio (CFR)

The case-fatality ratio measures the proportion of deaths4 among confirmed measles cases. It should be calculated for the community as a whole as well as hospitals. In the community, the CFR may be underestimated as many cases may die at home and where deaths are not reported. A high CFR in hospitals may be interpreted in many different ways. For example, that case management is not effective, or that mainly severe cases or those in extremis seek hospital care. If a more accurate estimate of the CFR is required, a carefully conducted community-based study should be undertaken. The formula for calculating CFR can be found in Annex 3, and where possible CFR should be estimated by different age groups.

Vaccine effectiveness (VE)

VE measures the effectiveness of vaccination in conferring protection against measles. The information required and formula for calculating VE is outlined in Annex 3.

For a more detailed analysis, a case-control study is needed to elucidate more specific risk factors, such as age at vaccination, number of doses received, access to care and travel history. Cases and controls (persons without measles) are identified and then compared to determine to what extent they differ, e.g. by age, sex, vaccination status, etc. To obtain assistance for such a study, district officials should consult with epidemiologists at the provincial and national level.

4. Interpret data

Generally, the initial descriptive analysis of person, time and place will help define who is at risk of measles and which areas are affected. In addition, data on the age of cases and their vaccination status will help to identify causes of the outbreak and the population that is at highest risk. This information is needed to guide the response activities, for example, defining the population and the age groups to be targeted for vaccination. When interpreting data, it is important to take into consideration the quality of the surveillance system generating the data, as reliable information is needed to guide action.

F. Implementing control and preventive measures

1. Managing cases and contacts to limit spread

As discussed in section B above, it is important to ensure adequate clinical management of measles cases in order to reduce measles mortality. In addition, if time and resources permit, the following measures should be implemented, as follow-up of all cases and contacts may not be possible if the epidemic is large and if resources are limited.

Health staff should report all patients in whom they suspect measles. Monitoring and follow-up of suspected cases includes the following measures.

• Limiting contact to only immediate family members who have been vaccinated or have prior history of measles. In particular, avoid contact with infants or young unimmunized children in the household.

• Suspected cases should not be hospitalized, unless they have complications or another condition requiring hospitalization, because of the high risk of intra-hospital transmission.

• Patients with measles who require hospitalization should, if possible, be isolated from onset of prodromal symptoms until five days after rash onset; health staff in contact with these patients should use respiratory precautions during this period

• Contact should be limited in outpatient departments (OPDs) such as waiting rooms, where there are suspected cases. For example, where feasible, separate segregated waiting areas and examination rooms for suspected cases should be set up in outpatient clinics.

Also, where feasible, officials must be prepared to identify persons who have had contact with a confirmed measles case and take the following actions to minimize spread.

• Contacts without written evidence of measles vaccination should be vaccinated and the symptoms of measles should be explained to them.

• During the second week after exposure, and at the first sign of possible measles (fever, runny nose, cough or red eyes) the contact should be instructed to stay at home.

2. Conducting appropriate vaccination activities

The district level Outbreak Coordinating Committee responsible for outbreak response should determine the appropriate vaccination activities following the steps outlined in Annex 2.

As soon as an outbreak is suspected, steps (a) and (b) below should be undertaken concurrently. In addition, as soon as the outbreak is confirmed, the district Outbreak Coordination Committee should review risk-assessment results and decide accordingly whether to continue with the selective vaccination activities or to carry out a non-selective vaccination campaign (see Figure 1).

a. Selective vaccination activities

As soon as a measles outbreak is suspected, the following steps should be taken.

1. Enhance social mobilization activities to inform the affected communities about the suspected outbreak, which specific age group of previously unvaccinated children is targeted for measles vaccination, and where parents should bring their at-risk children for vaccination.

2. Vaccinate all children (six to 59 months of age or determine the target age group according to the local disease epidemiology) presenting to a health facility or an outreach vaccination site without a history of measles vaccination (either written or verbal). Children receiving measles vaccine before the age of nine months must be revaccinated after the age of nine months (with at least a one-month interval between the doses). Note that in these mortality reduction settings the majority of measles cases occur in children under 5 years of age (21, 26).

3. Vaccinate hospital staff at risk of exposure who have not been vaccinated.

4. Ensure sufficient supplies. Use stock management records to determine available quantity and location of vaccine, auto-disable (AD) syringes and other supplies (e.g. cold-chain equipment and vitamin A) that are available immediately for use. Estimate and request the additional supplies needed so that activities are not interrupted due to supply stock outs.

b. Reinforcement of routine vaccination

A measles outbreak provides the opportunity to identify programme weaknesses causing the outbreak and a chance to correct them. As soon as a measles outbreak is suspected, and before laboratory confirmation of the suspected measles cases, the following steps should be taken to reinforce routine vaccination.

1. District staff, health-facility staff and partners should rapidly identify priority areas within the affected district (e.g. communities with low vaccination coverage and at high risk of morbidity and mortality).

2. Jointly work on strengthening the available district immunization workplans.

3. Locate health centres conducting immunization sessions that may need additional staff or vaccine supplies.

4. Organize corrective measures such as additional outreach services to communities with a high proportion of unreached children.

c. Non-selective mass vaccination activity

As soon as the outbreak is confirmed, and if the risk-assessment results indicate that there is a high risk of a large measles outbreak, then the capacity to carry out a high quality large-scale immunization campaign should be rapidly evaluated. That is:

• evaluate the availability of staff and financial resources (both internal and external) for the operational and logistical aspects of the campaign;

• evaluate if the vaccine and other supplies can be made available within the timescale necessary.

Carry out a safe and timely vaccination campaign in the targeted areas (affected and neighbouring areas as determined by the risk assessment) as soon as there is sufficient capacity (human and financial resources and vaccine and other supplies).

However, if the outcome of the risk assessment does not indicate a mass vaccination response, then selective immunization of unimmunized children presenting to health facilities as outlined in step (a) above should be continued, and the number of reported cases closely followed to monitor the progression of the outbreak.

For the non-selective mass vaccination response, the timing, target age group and area for vaccination, should be defined as outlined below. An accelerated micro-planning exercise should be performed to determine the bundled vaccine, logistics, staffing and communications needs for the campaign. Existing country or regional guidelines for conducting mass measles vaccination campaigns should be used (see the WHO Regional Office for Africa: measles SIAs field guide (27).

Timing of intervention: Once the decision to intervene has been made, it is critical to act as quickly as possible to minimize the number of severe measles cases and deaths.

The timing of the intervention plays a key role in the number of cases and deaths that may potentially be prevented. For example, Figure 2 shows the epidemic curve for N’djamena in the Republic of Chad in 2004–2005. An intervention was proposed at the beginning of the epidemic, and in the middle, and was finally implemented about five months after the start of the epidemic. Had the intervention occurred earlier, it is clear that its impact would have been greater. Even though it occurred late in the epidemic, the intervention may have contributed to improving population immunity, shortening the duration of the outbreak and preventing some severe cases and deaths.

Figure 2

The epidemic curve for N’djamena, Chad in 2004–2005.

Target population

Choosing the target population depends upon the susceptibility profile of the population. Key elements to consider are:

1. routine vaccination coverage and coverage during SIAs in each birth cohort;

2. age-specific attack rates;

3. absolute number of cases.

For example, Table 4 shows the attack rates and population and number of cases during an epidemic in Niamey, the Republic of the Niger, in 1995. The highest attack rate occurs in the 6–8 month age group. Although the attack rate in the 5–14 year old age group is much lower, the absolute number of cases in this age group is almost 25%. It is important to consider both absolute numbers of cases and the potential at-risk population, as well as the attack rate. In this example, the 5–14 year old age group may also contribute to transmitting the disease to younger age groups and so could be targeted for vaccination.

Table 4

Measles attack rates (AR) by age groups in Niamey, Niger, 1 January – 7 May 1995.

It is critical that the results from the outbreak investigation and prior surveillance data be used to develop and tailor an appropriate and logical response, e.g. to determine additional age and risk groups to be targeted for vaccination. If, for example, the data suggest that older children are affected, then the age group initially targeted for vaccination should be adjusted to include older cohorts. All age groups contributing to cases should be considered for vaccination. Even if the attack rate is low in some age groups, especially in older groups, they may represent a large proportion of cases and large potential groups at risk of both contracting measles and subsequent complications, or of transmitting the infection to younger persons. Once the age group targeted for vaccination is determined, all children in that age group should be vaccinated regardless of their vaccination status.

Target area

The response should target both outbreak-affected areas and adjacent areas in which the risk-assessment shows a high risk of spread. As distinct from preventive SIAs (e.g. catch-up and follow-up campaigns) that target whole countries, provinces or states, campaigns done in response to outbreaks should be more limited in scale.

Health staff should pay particular attention to ensure that groups and areas with a high likelihood of not being reached (i.e., with known low coverage) and at high risk for measles-related complications are reached during the vaccination activities, and any necessary supplemental measures such as the provision of vitamin A are provided. These vulnerable groups and areas include:

• young children, particularly those under one year of age;

• malnourished and vitamin A-deficient children;

• infants and children of HIV-infected women, and other immunocompromised children;

• certain ethnic and religious groups who may have poor access to immunization;

• populations with poor access to health care;

• staff at hospitals and other health facilities;

• All children above six months of age who are attending hospitals (inpatients and outpatients) or who are visiting the hospital.

Children receiving measles vaccine before the age of nine months during a campaign must be revaccinated after the age of nine months (with at least a one-month interval between the doses), since the efficacy of vaccine administered before nine months of age is likely to be low. Strategies to ensure that these children receive a second dose of measles vaccine include the following steps:

• informing mothers at the time of vaccination that their child must be vaccinated again;

• notifying health workers, NGOs and the community, about the need for these infants to receive a second dose.

Target Coverage

Ideally, the target coverage (the proportion of the target population you want to vaccinate) should be 100%. However, although this may not always be possible given available resources, the intervention should be conducted, even if it is not possible to achieve 100% coverage. Once the vaccination activities are conducted, it is important to carry out rapid coverage monitoring to estimate the coverage achieved, and to identify potential groups of missed children and ensure that they are vaccinated.

G. Ensuring effective community involvement and public awareness

When an outbreak is confirmed, there is likely to be widespread public concern and media attention. It is important to keep the public informed, to calm fear and encourage cooperation. Messages to the community should be clear and concise, using local terminology, and should convey the following:

• existence of an outbreak and the benefits of measles vaccination;

• signs and symptoms of the disease;

• encouragement to parents whose children have had a recent rash and fever illness to consult a health-care facility early after symptom onset;

• instruction to parents to bring their children to a health facility/vaccine post for vaccination;

• information on locations and opening hours of health facility/vaccine posts.

Messages to the community can be transmitted by radio and/or television, newspapers, posters and fliers, meetings with health personnel, community, religious and political leaders, and presentations at markets, health centres and schools. The media are useful partners in keeping the public informed through regular press releases and conferences. Select and use a community spokesperson to serve as focal person for the media. As soon as the outbreak has been recognized:

• tell the media the name of the spokesperson, and that all information about the outbreak will be provided by the spokesperson;

• release information to the media only through the spokesperson to make sure that the community receives clear and consistent information.

Meet with the spokesperson on a regular basis to give:

• frequent, up-to-date information on the outbreak and response;

• clear and simple health messages for the media to use.

4

A measles-related death is a death in an individual with a confirmed (clinically, laboratory-confirmed or epidemiologically) case of measles in which death occurs within 30 days of rash onset and is not due to another unrelated cause e.g. a trauma or chronic disease.

How is a measles outbreak managed?

Which field of CHN practice is delivered within official or government agencies?

Which level of health facility is the usual point of entry of a client into the health care delivery?