Epidemics and endemic diseases ll Prof. Hamed Adetunji

A timeline of major pandemics transmissible through the respiratory tract The Lancet Infectious Diseases , DOI: ( /S (14) ) Copyright © 2014 Elsevier Ltd Terms and Conditions Terms and Conditions

Burdens of Infectious Diseases worldwide

Some of the reasons for the difficulty in combating infectious diseases New infectious diseases continue to emerge Old infectious diseases increase in incidence or geographical distribution Old infectious diseases previously under control begin to re- emerge Potential for intentional introduction of infectious agents by bioterrorists Increasing resistance of pathogens to current antimicrobial drugs Breakdowns in public health systems and communication between nations

Middle East respiratory syndrome coronavirus (MERS-CoV) – Saudi Arabia Between 22 and 27 January 2016, the National IHR Focal Point for the Kingdom of Saudi Arabia notified WHO of 5 additional cases of Middle East respiratory syndrome coronavirus (MERS-CoV) infection.

What do you understand by the term ‘Epidemic’ or ‘Outbreak’?

Solution: An epidemic (or outbreak) is the occurrence of a disease in excess of what is expected in a particular community, for a particular groups of people, within a certain period of time

Other Terms Endemic it refers to the constant presence of a disease or infectious agent within a given geographic area or population group. It is the usual or expected frequency of disease within a population Pandemic refers to an epidemic occurring simultaneously in multiple locations world-wide

Common Epidemic likely diseases Diarrhoeal diseases including watery diarrhoea, Cholera, dysentery and typhoid are likely to occur in many regions Outbreaks of immunisable diseases like measles can be common if immunisation coverage is low Malaria is endemic in most parts of Sub Saharan Africa especially in low land areas; however outbreaks can occur in both low and highland areas

Familiarizing Data by Time Epidemic Curves

Descriptive Epidemiology: Time

An epidemic curve (epi curve) is a graphical description of the number of cases of illness by the date of illness onset Can provide information on the outbreak’s: Pattern of spread Magnitude Outliers Time trend Exposure and / or disease incubation period

Epi Curve: Pattern of Spread The overall shape of the epi curve can reveal the type of outbreak (the pattern of spread) Common source Intermittent Continuous Point source Propagated

Common Source Outbreak People are exposed to a common harmful source Period of exposure may be brief (point source) long (continuous) or intermittent

Epi Curve: Common Source Outbreak with Point Source Exposure Pattern of Spread

Epi Curve: Common Source Outbreak with Continuous Exposure Pattern of Spread

Epi Curve: Common Source Outbreak with Intermittent Exposure Pattern of Spread

Epi Curve: Propagated Outbreak Pattern of Spread

Epidemic Curves: Magnitude of the Outbreak Magnitude

Epi Curves Provide Information about the Time Trend of an Outbreak Date of illness onset for the first case Date when the outbreak peaked Date of illness onset for the last case Number of cases Days

Clues from the Epi Curve Incubation period The time from the moment of exposure to an infectious agent until signs and symptoms of the disease appear Period of exposure Point source outbreak Timeframe during which the exposure likely occurred

Using Epi Curves to Estimate the Incubation Period Use when timing of exposure is known and agent is unknown Estimated incubation period is between Time of suspected exposure Time of peak of epi curve

Using Epi Curves to Estimate Period of Exposure Use when incubation period for the disease is known Period of exposure is between Peak of epi curve counting back the average incubation period Earliest case, counting back the minimum incubation period

Centers for Disease Control. Hepatitis– Alabama. MMWR 1972:21: Calculating the Exposure Period

Creating an Epidemic Curve Cases of Disease X in Y Population, Nov-Dec 2012 Number of cases of disease reported during an outbreak plotted on the y-axis Time or date of illness onset plotted on the x-axis Pre-epidemic period included to show the baseline number of cases

Creating an Epidemic Curve Cases of Disease X in Y Population, Nov-Dec 2012 Descriptive title Axis labels

Epi Curve X-axis Units Depends upon the incubation period Begin with a unit one quarter the length of the incubation period Example: 1. Mean incubation period for influenza = 36 hours x ¼ = 9 3. Use 9-hour intervals on the x-axis for an outbreak of influenza lasting several days

Epi Curve X-axis Units For an unknown incubation period Graph several epi curves with different time units Choose units that best represent the data Units may range from hours to months, depending on the outbreak duration and known or suspected incubation period

Session Summary Outbreak The occurrence of more cases of disease than expected for a given place and time Outbreak investigation Decision to investigate depends on several factors Verification of the diagnosis allows for identification of the incubation period and is necessary to hypothesize about the exposure Case definition classifies case-patients related to the outbreak and is used to conduct additional case finding

References and Resources Centers for Disease Control and Prevention (1992). Principles of Epidemiology, 2 nd ed. Atlanta, GA: Public Health Practice Program Office. Centers for Disease Control and Prevention. Outbreak of Meningococcal Disease Associated with an Elementary School- -Oklahoma, March 2010; MMWR April 6, 2012 / 61(13); s_cid=mm6113a1_w s_cid=mm6113a1_w Centers for Disease Control and Prevention. Brainerd Diarrhea. Division of Bacterial Disease; October g.htm g.htm FOCUS Workgroup. An Overview of Outbreak Investigations. FOCUS on Field Epidemiology (1):1.