Abstract
This paper is a critical review of a research article involving the use of simulation to determine factors that contribute to the spread of measles when a person within a given area contracts the disease. The paper is divided into five sections, and each addresses a different aspect of the research article. The introduction states the research problem and explains why it is important to nursing. The methods section discusses the study design and how it fits the purpose of the study. It also describes the sampling procedure and protocol. The results section discusses the study’s findings. The discussion section explains how the study’s findings relate to the stated purpose, while the last section covers the overall presentation and the final summary of the article.
Introduction
The research problem is clearly stated in the paper. According to the authors, cases of measles continue to be reported in the United States even after endemic measles transmission was eliminated from the country. For example, on January 23, 2015, 68 measles cases were reported in California after people visited two Disney theme parks (Liu et al., 2015). In 2013, an unvaccinated adolescent visited London, and upon return to New York, he had contracted the disease, and it led to 58 reported cases of measles, which was the largest outbreak in the country since 1996 (Liu et al., 2015).
Therefore, the research problem is linked to this scenario and the need to identify factors that contribute to the occurrence of measles epidemics. This problem is important to nursing because after understanding how measles spreads, care providers can be in a position to prevent occurrences and be prepared to address any outbreaks in case they happen. This study is justified because the circumstances under which the tracing of individuals affected during an outbreak and other associated intervention measures given by different health departments to control measles epidemics are not known. Therefore, this study would fill this knowledge gap.
The study’s purpose is stated clearly – “to identify the characteristics of population vaccination coverage, clustering of susceptibility, individuals’ behaviors, and the public health response that impact the occurrence of measles epidemics” (Liu et al., 2015, p. 2). The theoretical or conceptual framework used for the study was not mentioned, but it is implied. The authors argue that identifying factors that contribute to measles epidemics could enable the relevant authorities to create a framework to prevent and address measles epidemics if they occur.
The implied framework helps in the achievement of the research objectives, and thus the two are linked. The literature review is current even though in 2015 when the current study was published, some sources were older than ten years. Sixty-two references were used, and nine of them were published in the 1990s. Of the remaining sources, fifteen were published within five years while the rest were published in the 2000s. The literature review section is missing. However, the authors gave a background section, which could be taken to represent the literature review.
The literature review is organized logically to support different sections of the paper. Additionally, the literature review supports the need for the study adequately. The authors used this section to discuss the need for having this study based on the documented evidence that measles outbreaks continue to be reported in the US especially among communities with minimal levels of herd immunity due to the lack of vaccination for various reasons.
The literature review also highlighted the problems associated with tracking down individuals affected with the disease and other intervention measures taken to control the spread of measles and prevent epidemics. For instance, the authors noted that health officials might not be in a position to identify possible infections and the contact persons in time for post-exposure prophylaxis to be useful in case of an outbreak.
Methods
The study used a simulation-based research design. This design, albeit uncommon in conventional research, fits the purpose of the study. The simulation model used was agent-based whereby transmission of measles was studied after the introduction of one index case into a specified synthetic population. Therefore, this design fits the purpose of the study as it allowed the authors to study the effects of public health interventions, such as contact tracing, when measles epidemics occur.
The design is linked to the sampling method and statistical analysis. The sample used is drawn from a synthetic population of participants drawn from the Synthetic Population Database maintained by RTI International. The analysis used Latin Hyperbole sample parameters to simulate one year of transmission after the introduction of the index case. Therefore, the analysis and sampling procedures are linked to the simulation-based research design of the study.
Due to the nature of the study, the sample involved parameters, and in this study, a Latin Hyperbole sample of 1024 parameter sets was selected. The four major parameters chosen for this study included ”
- vaccination coverage,
- level of immunity clustering (Ω),
- intervention delay, and
- contact finding probability to explore factors which contribute to the successful control of measles (i.e., the probability of uncontrolled measles outbreak)” (Liu et al., 2015, p. 7).
The sampling procedure is discussed in detail, but the authors did not justify the size of the sample.
The study protocol involved a synthetic population representing all individuals within California based on the U.S. Census and the California Department of Finance population estimates. Daycares were added to the synthetic population in a bid to capture the transmission of measles among pre-schooled children in the region. Additionally, the research protocol entailed simulations to cover the four parameters used for the study. First, to investigate the contact network and transmission, the simulation was based on interactions among people in various locations in California. To assess clusters of immunity, model clusters of susceptible individuals were created. Similarly, another model was created to simulate contact tracing and public health intervention strategies.
The instruments described in the article are the Latin Hyperbole parameters. Each parameter measures the concept it was intended to measure. In other words, the concept definition is consistent with the operational definition. For example, the contact network and transmission measured how measles transmission occurs following the interaction of individuals in a specified area. Similarly, the clusters of immunity parameters measured the level of vaccinations against measles in different regions across California. The authors did not present information on the reliability and validity of the instruments used for this study.
To address the threats of internal and external validity, which are inherent in the study design, the authors carried out sensitivity analysis. This step sought to establish the appropriate and useful parameters in determining the “number of secondary cases, the outbreak size, and the probability of uncontrolled outbreak in a one year of measles transmission” (Liu et al., 2015, p. 7). For each parameter set, 256 replications were computed.
The authors indicated that the Committee for the Protection of Human Subjects at the California Department of Public Health reviewed the project and established that it did not involve human subjects. Consequently, there are no indications of any ethical concerns. The study is discussed in enough detail for replication. For definiteness, the authors chose Humboldt County in California, with a population of 118,261 persons, and simulations were done based on each individual. This study population is large enough for the generalization of results in other set-ups.
Results
The characteristics of the sample are described thoroughly. The chosen synthetic population represented every person in the targeted geographical location. Demographic data, such as age and sex, for all individuals used in the simulation and their respective locations for social activity (workplace, school, neighborhood, and household) were collected for this study. The authors did not indicate the research questions or hypotheses.
However, one research question could be derived from the study’s purpose, and it was answered independently. The data collected for this study included contact networks and transmission based on vaccination coverage, the clusters of immunity, contact tracing, and public health intervention measures taken to address an outbreak.
For data analysis purposes, the simulated model was analyzed in two steps. The first one was the selection of a Latin Hypercube sample (38,39) containing parameters picked from the given ranges. For each parameter set, the epidemic was replicated 256 times. The partial rank correlation coefficient (PRCC) (40,41) was computed between each input parameter and simulation outcomes. Scenario analysis was also carried out for the four chosen parameters. Tables were used to present data, such as parameters being investigated including vaccination coverage and immunity threshold. The text supplements the data in the tables by discussing what different values mean within the overall context of the research.
The findings indicated that the level of vaccination coverage against measles and the clustering of immunity are key characteristics that determine public health preparedness and the ability to control epidemics. On vaccination coverage, if the number of individuals vaccinated against measles within a given area is over 95 percent, the chances of an outbreak, if one individual is exposed to the disease, are low.
However, if the level of vaccination coverage is less than 85 percent, outbreaks are likely to occur after an individual within the region is exposed to measles. The level of vaccination coverage is directly proportional to the herd immunity or immunity clustering. The level of public health preparedness to trace individuals that have contracted measles for the appropriate intervention measures also contributes significantly to the spread of the disease. For instance, if the response is delayed and contact individuals cannot be traced immediately, the risk of an outbreak increases significantly.
Discussion/Implications for practice
The authors relate the findings to the study’s purpose. For example, the authors conclude that their findings prove that the levels of vaccination coverage and herd immunity are major characteristics that determine the spread of measles within a given geographical location. The findings of the study are similar to those from previous studies. According to the authors, previous mathematical epidemiology studies had concluded that vaccination coverage and herd immunity played an important role in the control of the spread of measles during an outbreak. However, the authors did not discuss the findings that conflict with previous work.
The limitations of this study include the lack of enough empirical evidence for the majority of the behavior-related parameters used in this model. Additionally, the stochastic agent-based model used in this study does not allow for the different intervention measures that can be taken during a response to an outbreak. For instance, children aged between six and eleven months could get one dose of MMR vaccine as opposed to intramuscular IG within 72 hours of exposure provided the child would get another vaccination within 12 months. Finally, the study considered vaccination clustering among individuals aged less than 18 years.
Therefore, information on adult vaccination clustering is missing. Additionally, the model’s contact network did not consider healthcare settings, and thus critical information on the intervention measures might be missing, which affects the reliability of the results. The new research that has emerged is that another study could be carried out using data collected from real-life cases as opposed to a simulation. The study’s findings could be potentially used in nursing practice to ensure that public health departments are prepared to prevent the occurrence of epidemics and address any outbreaks that may arise.
Overall Presentation and Final Summary
The title accurately describes the type of study, major variables, and the target population. From the title, the reader notices that the study investigates the role of different factors, such as individual behaviors, vaccination, and public health response, in the process of controlling measles outbreaks using simulation for California. Additionally, the abstract accurately represents the study. It is divided into different sections including background, methods, results, and conclusions.
Therefore, looking at the abstract the reader can know the purpose of the study, the methods used in data collection, results, and the conclusions made by the authors. The report is logically consistent, as the authors present a research problem, and then proceed to carry out a study to prove or disprove their thesis. Additionally, the writing style is clear and concise as the language used is simple, and thus a wide audience can read and understand the study.
Reference
Liu, F., Enanoria, W. T., Zipprich, J., Blumberg, S., Harriman, K., Ackley, S. F., … Porco, T. C. (2015). The role of vaccination coverage, individual behaviors, and the public health response in the control of measles epidemics: An agent-based simulation for California. BMC Public Health, 15(447), 1-16. Web.