Outbreak Management: The SARS Outbreak in Epiville

Outbreak Management: The SARS Outbreak in Epiville
D. Background of the Epiville SARS Simulation outbreak
The case definition is a list of specific criteria used to decide whether or not one has the disease under investigation. The case definition of the Epiville SARS outbreak is a visitor to, or resident of the Amoy Apartment Complex or a worker at Star Hospital, who has onset of respiratory flu-like symptoms (high fever, cough, difficulty in breathing) from 10th August 2003 to 23rd August, 2003, without other apparent cause. The Epiville General Hospital suspects that the strange disease is the severe acute respiratory syndrome (SARS) although they are yet to conduct diagnostic tests to confirm the same. A clinical case is defined as an acute respiratory illness lasting ? 2 weeks and with onset from 10th August 2003 without other apparent cause for a person living in the Amoy Apartment Complex. A suspected case is a clinical case epidemiologically linked to a clinical case through a common household residency. All other clinical cases are considered probable.
The choice of case definition influences the scope of an outbreak investigation. For instance, if the case definition is too broad, the epidemiologist will include in their investigation all other illnesses that meet the stated clinical criteria (CDC, 2012). On the other hand, if the case definition is too strict, the investigation will only include people confirmed to have the disease (CDC, 2012). In the Epiville outbreak, for instance, the case definition includes both residents of, and visitors to the Amoy Apartments complex - implying that the epidemiologist will have to focus their outbreak investigation on both residents and visitors. On the other hand, if the case definition only considered residents, the investigation would not bother with non-residents and would only focus on the population living within the Complex.
Factors to Consider when Developing a Case Definition
The epidemiologist considers several factors when formulating a case definition. These are:
i) Person – demographic characteristics of the affected population including their age, sex, occupation, and race
ii) The geographical coverage of the suspected outbreak (place) such as the healthcare facility, street, town, or apartment complex
iii) The time representing the onset of illness in days, weeks, months, or years. Delineating the time period helps to exclude similar illnesses that are not related to the outbreak under investigation
iv) The clinical features associated with the illness under investigation, such as symptoms
v) Whether or not confirmatory laboratory tests have been carried out – this helps in grouping cases as either confirmed, probable, or suspected
vi) The aim of the outbreak investigation for which the case definition is developed – for instance, if the aim of the investigation is to know if anyone in a particular area has symptoms of a communicable disease so that they can begin planning on what actions to take, the case definition may be broad to identify all possible cases (CDC, 2012). However, if the aim of the investigation is to determine the causes of an outbreak, a strict case definition may be adopted to ensure that only people confirmed to have the disease are included (CDC, 2012).
Epiville SARS Simulation Outbreak in terms of PPT
Elements
Descriptive Variables
The Epiville Outbreak
Person
Age group, sex, occupation, race, and exclusion criteria of the affected population
The outbreak disproportionately affects older individuals aged over 50
Place
Geographical location
Facility
The outbreak is localized within Amoy Apartment Complex and Star Hospital
Time
Onset of illness
between 10th August 2003 and 23rd August 2003
The Epiville SARS outbreak is localized within the Amoy Apartments complex and Star Hospital, with an onset from 10th August to 23rd August 2003, and disproportionately affects older individuals above the age of 50
Steps in the Epiville SARS Outbreak Investigation
i) Define the epidemic by defining the clinical cases, the population at-risk of illness, and calculating attack rates
ii) Examining the distribution of cases by person, place, and time – the epidemiologist does this by reviewing charts of patients, creating lists of names of patients who have died from the disease to identify the patients’ profile, including their residence and age group.
iii) Look for combinations/interactions of relevant variables
iv) Developing hypotheses about the cause of the illness based on existing knowledge of the disease and relationships to diseases whose etiology is known
v) Testing the hypotheses through conduction of an appropriately-designed study and collection of additional data if necessary
vi) Recommend control and management measures such as quarantine, isolation, and public sensitization on prevention and control
E. Summarize the techniques used in the Epiville SARS Simulation outbreak investigation
Surveillance Methods used to Ascertain Cases
Surveillance is the continuous collection and analysis of data on cases that is not necessarily followed by subsequent action. Surveillance methods used to ascertain cases include:
i) Review of case records including centralized disease registries and hospital discharge notes
ii) Microbial laboratory monitoring
iii) Hospital reporting of confirmed cases to the Department of Health
iv) Physical counts and visits to the Amoy Apartment Complex
v) Periodic telephone calls to healthcare facilities/individuals/laboratories
Number of Suspect and Probable Cases
Suspect cases are cases that demonstrate the clinical features associated with the disease, but have not undergone confirmatory tests. There are 53 cases that can be categorized as suspected cases in Amoy Apartments, after showing respiratory symptoms, but without laboratory confirmation. On the other hand, probable cases are suspected cases for which testing has turned out inconclusive (CDC, 2012). Of the 70 case showing symptoms, 53 are confirmed cases, while 5 of the remaining 17 had clear chest x-rays despite showing symptoms. 6 recovered within a week, signifying flu, and 6 had pneumonia. The 5 who show symptoms, but have clear chests and no other attributable causes could be established are categorized as probable cases Mode of Transmission for Amoy Apartment Complex and the Star Hospital
The mode of transmission at Amoy Apartments is person-to-person, where transmission occurs through the spread of droplets when an infected person sneezes, speaks, or coughs. Person-to-person transmission is the most likely mode of transmission at Amoy Apartments as it requires close proximity since droplets fall to the ground within a few feet. The cases occur close in time, shortly after attending the luau at Amoy Garden, where they were in close contact for hours. The transmission at Star Hospital also occurs directly through person-to-person – all the cases occur close in time shortly after the index case was admitted into the hospital. The fact that infections occur close in time indicates that the source of infection was the same for all infected persons. Further, the infected healthcare workers report that they were in close contact with the index patient during treatment. Infections are likely to have resulted from contaminated droplets when an infected person sneezes, coughs, or speaks.
Process used to develop the working hypothesis for this outbreak
Hypotheses are developed using one of two processes: based on what is known about the disease or based on the deducing insights from comparable diseases whose etiology is known. In the Epiville outbreak, the development of hypotheses is based on the little knowledge available about the disease. For instance, based on the little knowledge available on the nature of the transmitting agent and its incubating period, the epidemiologist is able to infer that the mode of transmission at Amoy Apartment and Star Hospital was direct person-to-person contact when an infected person speaks, coughs or sneezes.
F. Present your case control study design analysis
Identify an appropriate study design
A case-control study design would be more effective for the current outbreak at Epiville. A case study design divides the population into two groups that are identical, but which differ by disease status. The aim of the case-control design is to identify potential risk factors for the defined disease. Based on data from the disease registry, the epidemiologist could categorize the Amoy Apartments population into an exposure and control group. Data would then be collected and analyzed to determine the possible risk factors facing individuals in either group. As there still is little known about the disease under investigation, there is a need for a study design that provides crucial insights on potential risk factors to allow for better prevention and control measures.
Data to be collected
Data to be collected in the above study design includes: existing comorbidities, current medication, family conditions, and the severity of illness
Epiville Curve Simulation Outbreak Plot
The outbreaks at both Amoy Apartments and Star Hotel are represented by the person-to-person/propagated epidemiology outbreak curve. The mode of person-to-person transmission is evidenced by the fact that the infections occur close together. The infections occur over a span of 10 days in the case of Amoy Apartments and over a span of 13 days at Star Hotel.
Agent Incubation Period and why it is important to know the incubation period
From the curves, the individual that got infected on the 17th most likely infected the one who began to show symptoms on the 20th, who is then likely to have infected the one whose symptoms begin on 23rd in Star Hotel. At the same time, from the Amoy Apartment Epiville curve, it is likely that the individual who got infected on the 10th infected the one who began to show symptoms on the 12th - a span of 2 -3 days. Considering that individuals could have been infected some days before they fell ill on the dates reported, one could conclude that the agent has an incubation period of around 2 to 20 days. Understanding the incubation period of an agent is crucial as it helps the epidemiologist to know when an infected individual is likely to be asymptomatic and when they are most likely to spread the disease (Giessecke, 2017).
Difference between epidemic, endemic, and pandemic
An epidemic is the occurrence of an illness or outbreak in a defined region or community, whose frequency is in excess of normal expectancy (Giessecke, 2017). An infection is said to be endemic when the infection is maintained at the same baseline level for a prolonged period (Giessecke, 2017). When an epidemic spreads across national boundaries, into multiple countries, it is referred to as a pandemic. The Epiville outbreak is in the epidemic stage. First, the infections are localized within the Amoy Apartment complex and the health facilities that infected individuals visit for treatment. There is no evidence to indicate that the illness spread outside the area. Further, the illness meets the criteria for epidemic disease - Mr. Jones, one of the managers at the Amoy Complex, explains that the complex has experienced a series of outbreaks recently, but the frequency of the current outbreak is more conspicuous given that over 70 people had reported symptoms in less than a week.
Case fatality rate and its significance
The case fatality rate is the proportion of people who die as a proportion of those who get ill (Giessecke, 2017). Number of confirmed SARS cases from the Amoy Apartment complex was 53. Of these, 12 died.
The case fatality rate = = 0.22
The case fatality rate shows how deadly a disease is; the higher the case fatality rate, the deadlier the disease.
Primary and Secondary Attack Rates
The attack rate measures the number of confirmed cases as a proportion of those exposed to the risk. The primary attack rate is the attack rate at Amoy Apartments.
Primary attack rate = X 1000 = 88 cases of SARS in every 1,000 people in Amoy apartments
Secondary Attack rate = X 1000 = 200 cases of SARS per 1,000 people in Star Hotel
G. Discuss the management of the Epiville SARS simulation outbreak
One of the three principles of outbreak management
Outbreak management is the process of anticipating, preparing for, preventing, detecting, and controlling outbreaks to minimize their economic and health impact (Giessecke, 2017). Outbreak management is based on three principles: i) the average probability that a contact will get infected over the duration of relating with an infected person; ii) the average rate of getting into contact with an infected person, and iii) the average duration of infectiousness. The average rate of getting into contact with an infected person is measured by the average number of contacts an infected individual has per unit time (Giessecke, 2017). In a measles outbreak, it could be measured by the number of children one passes every day (Giessecke, 2017). In the case of the Epiville SARS outbreak, it could be the number of people one passes as they go about their duties within the complex.
Measures that should be implemented to control the SARS simulation outbreak
The probability that a contact will get infected (measured by the parameter k) is relatively high in Amoy as the complex houses 600 residents, implying a significant degree of individual social interaction. As such, the most plausible measures need to focus on reducing movement among infected persons and hence, ensuring minimal contact with uninfected persons. Quarantine and isolation are the most plausible measures as they minimize movement and limit contact between persons (Giessecke, 2017).
Rationale for recommending a specific surveillance type
Surveillance could take one of two types: active and passive surveillance. It is based on the idea that a physician may only have physical access to a few cases in an outbreak and may require access to the collected notifications on a national or regional level to understand the whole picture of the outbreak (Giessecke, 2017). Passive surveillance is regular reporting by different institutions that does not involve the active search for cases, but notifying a central location of the number of suspected and confirmed cases as well as tests conducted. However, active surveillance is more beneficial during an outbreak as it is proactive and does not just involve reporting what an institution has done, but also contacting other healthcare providers and laboratories to request information about a disease. It helps to portray a clearer picture of the outbreak as it provides better avenues for identifying the prevalence of suspected and confirmed cases within the greater population.
In conclusion, the processes of outbreak investigation and management were carried out effectively. First, the broad case definition that includes both residents and non-residents of Amoy Complex increases the scope of the investigation, reducing the likelihood that a positive case in the population would fail to be identified. Techniques employed in the outbreak management process include continuous surveillance and the development of effective working hypotheses to guide the investigation. In the end, quarantine and isolation were used to minimize movement in the most risky areas and, hence, reduce the risk of direct person-to-person transmission. The low case mortality rate could be an indicator that the disease is not very deadly. However, it could also be an indicator of the effective outbreak investigation and management. A crucial point of learning from the analysis is that the case definition forms the foundation for the outbreak investigation and the success of the investigation widely depends on it. Secondly, continuous surveillance is a crucial element in the investigation of an outbreak. However, to be effective, surveillance needs to be more proactive, with the researcher taking their time to call other stakeholders to ascertain cases and obtain more information about the outbreak. Finally, communication amongst key stakeholders is crucial as it ensures that all parties are on the same page.
References
CDC (2012). Lesson 1: Introduction to Public Health, Center for Diseases control and Prevention. Retrieved from https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section5.html
Giesecke, J. (2017). Modern Infectious Disease Epidemiology (3rd ed.). Boca Raton, FL: CRC Press.