Outbreaks of infectious disease
Outbreaks of infectious disease refer to instances when the occurrence of a specific disease exceeds what is typically expected in a particular community, whether that be a small setting like a school or a broader region such as a country. These outbreaks can be classified into three main types: endemic, epidemic, and pandemic. Endemic diseases have a consistent presence in a specific area, while epidemics are characterized by sudden increases in disease incidence within a region. Pandemics represent the most severe outbreaks, affecting a large geographic area and significant portions of the population, such as COVID-19 and the Spanish flu.
The determination of an outbreak relies on comparing current case numbers against expected incidence rates, which can be influenced by factors like population changes and reporting practices. Once an outbreak is confirmed, rapid control measures are critical. These can range from public education and vaccination efforts to immediate actions like recalling contaminated products when foodborne illness is involved. Recent outbreaks, including monkeypox and Ebola, illustrate the ongoing challenges in managing infectious diseases. The impact of these outbreaks extends beyond health, straining healthcare systems and affecting social and economic productivity, highlighting the importance of effective prevention and response strategies.
Outbreaks of infectious disease
Definition
The term “outbreak” denotes a larger-than-expected occurrence of a specific disease or infection during a particular time and in a certain place. In other words, an outbreak is present when disease levels are greater than what would be typical or expected in a given community. Such a community could be as small as a school or restaurant or as large as a nation or continent. Outbreaks also can occur globally.
Classification
Although some variation exists in the precise definition of “outbreak” and its patterns of occurrence, the following is a general guide to the various types of outbreaks.
Endemic. An outbreak is considered to be endemic when there is continual presence of a disease or infection within a specific geographic area or among a particular subpopulation. For example, malaria is endemic to certain parts of Africa.
Epidemic. An epidemic is the sudden and severe occurrence of a disease or infection within a particular region or subpopulation. Epidemics usually spread very rapidly. An example of an epidemic is acquired immune deficiency syndrome (AIDS) among users of intravenous drugs.
Pandemic. As with an epidemic, a pandemic involves the sudden and severe occurrence of a disease or infection that spreads rapidly. However, a pandemic affects a much larger geographic area (several countries or more) and a sizable proportion of the population. Although a pandemic is the most serious type of outbreak, it is relatively uncommon, having occurred just three or four times per century. Examples include the great influenza (Spanish flu), the Hong Kong flu, influenza A (H1N1), and COVID-19 (SARS-CoV-2).
Determining the Existence of an Outbreak
To establish whether an outbreak truly exists, it is essential to know the expected number of cases for a particular area during a given period. This may be done by comparing the current number of cases with the incidence rates in recent months or years. Sources of such information include health department surveillance records, disease registries, and hospital discharge records.
Even if the current number of cases appears to exceed the expected number, the excess may not necessarily indicate an outbreak. Variations in reporting procedures can impact these numbers, as can sudden changes in population size. Such factors must be considered when determining whether the increased number of cases would constitute an outbreak.
Implementing Measures of Control and Prevention
Once an outbreak is confirmed, control and prevention measures should be implemented immediately. Control methods can be undertaken quickly if the outbreak's source is known. For instance, if the outbreak is food-borne, a control technique would be to destroy or recall the contaminated products.
Control measures can also be directed at interrupting disease transmission and minimizing exposure to causative agents. Immunizations help reduce susceptibility to disease. However, developing effective vaccines can take time. Regardless of the methods used, educating the public is a major component of controlling and preventing outbreaks. As the COVID-19 pandemic proved exceptionally infectious and it became apparent that individuals could be asymptomatic and unknowingly transmitting the virus, federal and state governments worldwide took measures to encourage or even enforce the practice of "social distancing."
To limit social interaction and close contact (the major cause of the spread of COVID-19), people were asked or directed to remain at least a certain number of feet apart, to refrain from activities involving groups, and to avoid public places not deemed essential. Experts hoped this measure would reduce large amounts of patients who had contracted the disease from flooding hospitals at one time and limiting the availability of health care resources such as ventilators.
Recent Outbreaks
- Measles: In 2023, 10.3 million people worldwide were infected with measles, a 20 percent increase from the previous year. Fifty-seven countries experienced outbreaks in 2023 because of gaps in vaccine coverage.
- Marburg virus disease (MVD; 2023-2024) (formerly Marburg hemorrhagic fever): In 2023, outbreaks were recorded in Equatorial Guinea and Tanzania. In mid and late 2024, Rwanda experienced an outbreak of MVD.
- Mpox (formerly Monkeypox; 2021-2022): Confirmed by PCR in May 2021, the UK and Northern Ireland documented their first case of the disease, followed by the US in the fall. After 87,000 cases and 140 deaths in 111 countries, the outbreak slowed by May 2023.
- Ebola Virus Disease (August 2018-January 2020): Primarily problematic in the Democratic Republic of the Congo, this outbreak was a concern for the WHO through the end of 2022. It was the second-largest Ebola outbreak on record. The country was afflicted in the same year with cholera and Mpox.
- COVID-19 (December 2019): This outbreak was believed to have originated in China and was declared a public health emergency of international concern by the World Health Organization (WHO) in January 2020, and a pandemic by March was caused by a particularly transmittable novel coronavirus, severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2. The disease caused by the virus, COVID-19, impacted a large number of countries, with the United States, Italy, and Spain seeing some of the highest numbers of confirmed cases as of April 2020.
- Cholera in Haiti (October 2010): Before this outbreak, cholera had not occurred in Haiti for several decades.
- Salmonella (August 2010): Millions of eggs were recalled after thousands of people in the United States became ill from Salmonella enteritidis.
- Escherichia coli (July 2009): This outbreak, involving E. coli infection and beef products, occurred in the United States.
- E. coli (June 2009): This outbreak of E. coli infection in the United States was linked to the consumption of raw, refrigerated, and prepackaged cookie dough.
- H1N1 influenza (April 2009): Cases of the H1N1 flu were confirmed in the United States and internationally.
Impact
The overall impact of a disease outbreak is enormous. In addition to negatively affecting people’s health and well-being, outbreaks burden healthcare facilities and systems, often draining their resources. Control, prevention, and education must be further developed and implemented. Such efforts require substantial time, energy, financial resources, and collaboration among policymakers and other community groups. Outbreaks can also impact school and workplace productivity, creating extreme burdens for society.
Bibliography
Adams, David P. Foundations of Infectious Disease: A Public Health Perspective. Jones & Bartlett Learning, 2021.
"CDC Current Outbreak List." Centers for Disease Control and Prevention, www.cdc.gov/outbreaks/index.html. Accessed 5 Jan. 2025.
Chao, Dennis L et al. “School Opening Dates Predict Pandemic Influenza A (H1N1) Outbreaks in the United States.” Journal of Infectious Diseases, vol. 202, no. 6, 2010, pp. 877-80, doi:10.1086/655810. Accessed 5 Jan. 2025.
Christakis, N. A., and J. H. Fowler. “Social Network Sensors for Early Detection of Contagious Outbreaks.” PLoS One, vol. 5, no. 9, 2010, doi.org/10.1371/journal.pone.0012948. Accessed 5 Jan. 2025.
Collins, Francis. "To Beat COVID-19, Social Distancing Is a Must." NIH Director's Blog, National Institutes of Health, 19 Mar. 2020, directorsblog.nih.gov/2020/03/19/to-beat-covid-19-social-distancing-is-a-must. Accessed 5 Jan. 2025.
Dworkin, Mark S., editor. Outbreak Investigations around the World: Case Studies in Infectious Disease Field Epidemiology. Jones and Bartlett, 2010.
Gholamrezanezhad, Ali, and Michael P. Dube. Coronavirus Disease 2019 (COVID-19): A Clinical Guide. Wiley-Blackwell, 2023.
"History of Infectious Disease Outbreaks and Vaccines Timeline." Mayo Clinic, www.mayoclinic.org/diseases-conditions/history-disease-outbreaks-vaccine-timeline. Accessed 5 Jan. 2025.
"Measles Cases Are Rising – Here’s What Can Be Done." World Economic Forum, 29 Nov. 2024, www.weforum.org/stories/2024/11/measles-cases-rising-health-vaccines. Accessed 5 Jan. 2025.
Meehan Arias, Kathleen. Outbreak Investigation and Control in Health Care Settings: Critical Issues for Patient Safety. 2nd ed., Jones and Bartlett Learning, 2009.
Petersen, Eskild, et al. Infectious Diseases: A Geographic Guide. 2nd ed., John Wiley & Sons Inc., 2017.
Sherman, Irwin W. Twelve Diseases That Changed Our World. John Wiley & Sons, 2007.
Taylor, Derrick Bryson. "A Timeline of the Coronavirus Pandemic." The New York Times, 17 Mar. 2021, www.nytimes.com/article/coronavirus-timeline.html. Accessed 5 Jan. 2025.
Srinivasan, Arjun. “Influential Outbreaks of Healthcare-Associated Infections in the Past Decade.” Infection Control and Hospital Epidemiology, vol. 31, 2010, doi:10.1086/655987. Accessed 5 Jan. 2025.