Management of Epidemics

Incidence

• Incidence refers to the occurrence of new cases of disease or injury in a population over a specified period of time.

Prevalence

• Prevalence, sometimes referred to as prevalence rate, is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time. Prevalence differs from incidence in that prevalence includes all cases, both new and pre-existing, in the population at the specified time, whereas incidence is limited to new cases only.
• Point prevalence refers to the prevalence measured at a particular point in time. It is the proportion of persons with a particular disease or attribute on a particular date.
• Period prevalence refers to prevalence measured over an interval of time. It is the proportion of persons with a particular disease or attribute at any time during the interval.

Endemic

• Endemic refers to the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area.
• Hyperendemic refers to persistent, high levels of disease occurrence.

Epidemic

• Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.
• Outbreak carries the same definition of epidemic, but is often used for a more limited geographic area.
• Cluster refers to an aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known.

Pandemic

• Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people.

Enzootic

• Endemic in animals. An enzootic disease is constantly present in an animal population, but usually only affects a small number of animals at any one time.

Epizootic

• A disease in animal population analogous to an epidemic in humans.

Panzootic

• An outbreak of infectious disease of animals (epizootic) that spreads across large region, for example, a continent, or even worldwide.

Characteristics of epidemic outbreaks

• Excess number of cases for the time and place
• Increase morbidity & mortality
• Panic & confusion
• Economic & social disruption
• Overwhelming of resources
• Inability to cope
• Need for external assistance
• International stigma

• Build-up of susceptible population - low herd immunity, overcrowding
• Presence or impending introduction of a disease agent - healthy carriers, immigrants
• Mechanism of transmission - contaminated water, increase vector population
• Surveillance detection of cases - routine, active, sentinel

• Cerebrospinal meningitis
• Cholera
• Measles
• Yellow fever
• Lassa fever
• HIV/AIDS
• Poliomyelitis
• Corona virus diseases
• Ebola virus disease
• Other viral haemorrhagic fevers

Preparedness phase

• Set up EPR committee
• Have a response team
• Inventory of resources- manpower, materials, money
• Resource mobilisation
• Capacity building
• Early warning system
• Disease surveillance

Resource assessment

• Budgetary provisions
• Personnel
• Medical care
• Laboratory support
• Field teams
• Immunisation
• Communication

Sources of assistance

• WHO, UNICEF, UNHCR, WFP, UNDP, FAO
• MSF, CARE, Red Cross, Rotary
• Governments at all levels
• Community based philanthropists
• Volunteers

Response

• Ascertain reality of epidemic outbreak
• Check registers
• Community interviews
• Verbal autopsy
• Visit mortuaries
• Check burial grounds
• Make diagnosis
• Who, where, when, what, why, how?
• Case management/treatment of affected people
• Infection prevention & control/immunisation where appropriate
• WATSAN activities
• Health education/risk communication
• Data management
• Continuous feedback
• Relief operations

Mitigation

• Immunization
• Environmental sanitation
• Water supply
• Legislations
• Sensitization and awareness

Coordination

• Disease control committees & are mobilized, after receive information of the case

• Refugees
• Internally displaced persons
• Assylum seekers
• Fugitives
• Special migrants/emigrants

1. Precipitating causes of displacement
2. Duration of stay of refugees
3. Land tenure systems
4. Community acceptance
5. Supportive logistics
6. Security

1. Water supply
2. Food
3. Clothing
4. Housing/shelter
5. Security
6. Sanitation including defecation options
7. Medical care
8. Medications/drugs

1. Precipitating causes
2. Empowerment
3. Relationships with host communities
4. Rehabilitation

• Estimate the baseline population
• Determine the population at risk
• Document all affected cases
• Document all deaths
• Calculate the attack rate
• Calculate the case fatality rate
• Draw an epidemic curve
• Evaluate the impact of control measures
• Continuous surveillance

3 Main Indicators/Indices

1. Attack rate
2. Case fatality rate
3. Epidemic curves

Attack rate

(Number of people affected/Total number of people at risk) X 100, or 1000, or 100,000

• It is not everybody in a community that are usu. are risk. E.g. for measles persons are risks are children of age 5-15 years
• It is the measure of the herd immunity of the community; if the herd immunity is high, the attack rate will be low, and vice versa
• It is also a measure of the virulence of the organism; if virulence is high, attack rate will be high, and vice versa. The viral hemorrhagic fevers can have very high attack rate because of the high virulence of the causative organism

Case fatality rate

(Number of deaths/Total number of people affected) X 100

• Timeliness – refers to ‘reporting the case on time’ or ‘responding of the authority to the case on time’
• Adequacy – availability of sufficient response materials; drugs,
• Appropriateness – giving the Right tx/response e.g. giving fluids first before vaccine in treating cholera

Epidemic curves

• No. of cases is plotted against Time (hours, days, weeks); in massive food poisoning the time can be in hours (e.g during christmans)



• Two types
• Point-source epidemic curves – bell-shaped with a common/single point of exposure & a single peak (representing pt. of max. incidence). This is found in, for e.g., large no. of people presenting with food poisoning after attending a particular party (the common point of exposure)
• Propagated epidemic curve – multi-modal curve with multiple peaks. This is found in, for e.g., if infected persons come to a place and infected other people, and they in turn, infect another group of people

Practice Question

In a given community of 1500 people, measles outbreak affected 120 people with 40 death; Calculate (i) Attack rate; (ii) Case fatality rate

(Children <15 years are 45% of population)

• No. of People at risk = children < 15yrs = (45/100) X 1500 = 675
• No. of people affected = 120

Attack rate = (120/675) X 100 = 17.77%

Case fatality rate = (40/120) X 100 = 33.33%