Outbreak Definition for Reportable and Non-Reportable Diseases
Guidelines for Outbreak Control
Report a Potential Outbreak
What is an Outbreak?
General
The occurrence in a community, facility, workplace or region of a case or cases of an illness in excess of the number usually expected. The number of cases indicating an outbreak or cluster will vary according to the agent, disease, or condition, the site conditions and/or hazards, size and type of population exposed, previous experience or lack of exposure to the disease, and time and place of occurrence.
The number of cases indicating presence of an outbreak is disease specific.
Foodborne
An outbreak is defined as any clusters of illnesses in which two or more persons (usually residing in separate households) associated in time and place experience onset of a similar, acute illness (usually gastrointestinal) following ingestion of common food or drink (IDPH Principles and Procedures for Investigating Suspected Outbreaks of Foodborne and Waterborne Illness, 2004).
To determine if an outbreak is a confirmed outbreak, see the CDC Guide to Confirming an Etiology in Foodborne Disease Outbreak
Waterborne
An outbreak is defined as clusters of illness in which two or more persons (usually residing in separate households) associated in time and place experience onset of a similar, acute illness (usually gastrointestinal) following ingestion of drinking water or recreational contact with water. (IDPH Principles and Procedures for Investigating Suspected Outbreaks of Foodborne and Waterborne Illness, 2004).
Acute gastroenteritis (AGE) in a school or daycare setting
An outbreak is defined as four or more persons with acute onset of vomiting and/or diarrhea in a classroom or in an otherwise defined group of students; or cases in more than 10% of the school's/daycare's census in a single day. (IDPH Guidance for Prevention of Acute Gastroenteritis (AGE) Outbreaks in Daycare Facilities and Schools, 12/20/2011).
Conjunctivitis outbreaks
Ten or more clinical cases with a common epidemiological link if there is no etiologic agent identified. If an etiologic agent is identified 5 or more clinical cases would count as an outbreak if there is an epi link is present.
Fifth Disease
Fifteen epidemiologically-linked clinically compatible cases with onsets within a 15-day period.
Group A Streptococcus Invasive Disease Outbreak
Two or more confirmed epidemiologically-linked cases of GAS isolated from a sterile site within 4 months.
Group A Streptococcus Non-Invasive Disease Outbreak
Ten epidemiologically-linked persons with lab confirmed GAS (either sterile or non-sterile sites) with onsets within a 10-day period.
Hand, Foot, and Mouth Disease
Ten epidemiologically-linked persons with clinically compatible illness with onsets within a 10-day period.
Hepatitis A
Two or more non-household (single family households) cases epidemiologically linked by time and place. Cases within facilities such as homeless shelters should be counted as outbreaks and are not considered single family households.
Herpes simplex
Two or more suspect cases of herpes simplex epidemiologically linked within a 5-day period. If no laboratory testing is done, these would be suspect outbreaks.
Measles
Three or more epidemiologically-linked cases. Even one case of measles can be considered a potential outbreak.
Methicillin Resistant Staphylococcus aureus (MRSA) Infection
Clusters of two or more laboratory confirmed cases occurring in community settings (including, but not limited to schools, correctional facilities, day care and sports teams). Reportable by telephone or facsimile as soon as possible, within 24 hours.
For the purposes of this section, a MRSA cluster is defined as two or more laboratory confirmed cases of MRSA infection occurring in a community setting during a 14-day period for whom an epidemiological link is readily apparent to the reporter.
Methicillin Susceptible Staphylococcus aureus (MSSA)
Ten epidemiologically-linked persons with lab confirmed MSSA with onsets within a 10-day period.
Mumps
Three or more cases linked by time and place, with at least one lab confirmed by PCR (i.e., at least one confirmed and two probable epidemiologically-linked cases).
Pertussis in a school or childcare setting
Any cluster of five or more pertussis cases linked by time and place (within 42 days); household contacts may be included as long as at least one of the five cases is a non-household case. The outbreak case definition may be used to count cases if one case has been confirmed.
Scabies, Confirmed Outbreak
One case of healthcare provider-diagnosed Norwegian (crusted) scabies, or two or more symptomatic persons with epidemiologically-linked exposure and at least two are skin-scraping positive.
Scabies, Suspect Outbreak
Two or more symptomatic persons with epidemiologically-linked exposure
- AND none of the affected persons are diagnosed with Norwegian (crusted) scabies
- AND only one person is skin scraping positive
- OR healthcare provider diagnosis of scabies (either skin scraping is not performed or skin scraping performed with negative results) AND scabicide treatment is ordered for two or more persons.
Varicella
Three or more cases linked by time and place.
What is a Disease Cluster?
Disease Cluster for Investigation
Occurrence of more cases of a particular disease than expected for a given place and time or a number of ill people with similar signs and symptoms (or a diagnosis) whose symptoms have onsets in close proximity to one another in space and/or time.
Please note:
Acute respiratory illness (ARI) outbreaks e.g., COVID-19, influenza, RSV etc. are not reportable, however, can be discussed with KCHD if there are any concerns.
