Discussion: Antibiotic Resistance

One of the problems in medicine and epidemiology today is the emergence of superbugs or multi-resistant bacteria.  What are some of the factors that have contributed to antibiotic resistance?  What strategies would you propose to address this problem? 

Module 4 – Home

SCREENING FOR DISEASES

Modular Learning Outcomes

Upon successful completion of this module, the student will be able to satisfy the following outcomes:

• Case
  • Discuss the relationship between sensitivity and specificity.
  • Describe limitations of public health screening programs.
  • Examine and critique methodology used in epidemiologic studies.
  • Comprehend basic ethical and legal principles pertaining to the collection, maintenance, use, and dissemination of epidemiologic data.
  • Reflect upon and integrate course concepts.
• SLP
  • Discuss control measures and strategies for controlling the outbreak.
  • Make inferences regarding the source of contamination.
  • Evaluate the strengths and limitations of epidemiologic reports.
  • Prepare and submit a Reflective Essay.
• Discussion
  • Describe factors contributing to antibiotic resistance and potential strategies.
  • Reflect on course concepts.

Module Overview

Primary prevention is the desired objective in public health. When primary prevention is not possible, the secondary approach is early detection and prompt treatment of a disease (secondary prevention). There are two possible approaches to early diagnosis: 1) prompt attention to the earliest symptoms of disease and 2) detection of disease in asymptomatic individuals. During this module, we will focus on the second approach, the detection of disease in asymptomatic individuals.

Screening tests are the basic tool in the early detection of disease. Screening tests should provide a good preliminary indication of which individuals have the disease and which do not. This is referred to as validity. A screening test has two properties, sensitivity and specificity. The sensitivity of a test is how well the test will pick up on the fact that the person actually has the disease. Those who have a disease may either correctly test positive for a disease (true positive) or incorrectly test negative for a disease (false negative). The specificity of the test is how well the test does at being negative when the person does not have the disease. Those who do not have a disease may either correctly test negative for a disease (true negative) or incorrectly test positive for a disease (false positive).

An ideal screening test would be 100% sensitive and 100% specific. In practice, this does not occur. In fact, sensitivity and specificity are typically inversely related. That is, when sensitivity is increased the specificity decreases and when sensitivity is decreased the specificity increases.

Predictive Value

The ability to predict the presence or absence of a disease from test results is referred to as predictive value. It is dependent on the prevalence of a disease in the population tested, as well as the sensitivity and specificity of the test. The higher the prevalence, the more likely it is that a positive test is predictive of a disease.

Reliability

Reliability is defined as consistency in screening test results when the test is performed more than once on the same individual under the same conditions. Two major factors affect reliability: variability in the method (e.g., stability of reagents) and observer variation. These variations can be reduced by standardization of procedures, training of observers, and periodic checks on their work.

Yield

Yield is defined as the amount of previously unrecognized disease that is diagnosed and brought to treatment as a result of screening. The following factors affect the yield of a screening program:

• Sensitivity of the test
• Prevalence of unrecognized disease
• Frequency of screening
• Participation in screening and follow-up

Evaluation of Screening Programs

Because of the high costs and risks, screening programs should be conducted only when it has the potential to lead to a significant decrease in the rates of death or disability. Outcome measures such as the disease-specific death rate, physiological variables (e.g., blood cholesterol level), and case-fatality rate should be compared between screened and unscreened groups. The least biased method for evaluating a screening program would be a random, experimental study (i.e., randomly assigning individuals in a study sample to either a group that provides free screening or a control group).

Sources of Bias

Unfortunately, randomized, experimental studies are rarely done. Instead, observational studies are often conducted, which are subject to several different sources of bias:

• Lead Time Bias. Lead time is defined as the interval between a time a condition is detected through screening and the time it would normally have been detected by the reporting of symptoms. A screening test may lead to early detection without delaying the time of death, and as a result, the screened case group may appear to have a higher survival rate than the control group.
• Patient Self-Selection. Individuals who choose to participate in early detection programs may differ from those who do not in characteristics that may be related to survival. For example, participants may be more health-conscious, more likely to be compliant with prescribed therapy, etc.

Course Reflection

As your study of this course content draws to a close, it is important to step back and reflect on new levels of understanding, skills, and knowledge that were developed as a result of your efforts throughout this course. It is particularly important to reflect on the course outcomes (what you were intended to learn in this course).

Module 4 – Background

SCREENING FOR DISEASES

Required Reading

Brown, L. G., Hoover, E. R., Selman, C. A., Coleman, E. W., & Schurz Rogers, H. (2017). Outbreak characteristics associated with identification of contributing factors to foodborne illness outbreaks. Epidemiology and Infection, 145(11), 2254-2262. doi:10.1017/S0950268817001406

Castro, V. S., Carvalho, R. C. T., Conte‐Junior, C. A., &Figuiredo, E. E. S. (2017). Shiga‐toxin producing Escherichia coli: Pathogenicity, super shedding, diagnostic methods, occurrence, and foodborne outbreaks. Comprehensive Reviews in Food Science and Food Safety, 16(6), 1269-1280. doi:10.1111/1541-4337.12302

Center for Disease Control and Prevention. (2019). Steps in a Foodborne Outbreak Investigation. Retrieved from https://www.cdc.gov/foodsafety/outbreaks/investigating-outbreaks/investigations/index.html

Ghizzone, M., &Choko, A. T. (2019). Oral HIV self-testing kit demonstrates 100% specificity, 99.5% sensitivity. Infectious Disease News, 32(3), 20-20.

Hess, K. L., Fisher, D. G., & Reynolds, G. L. (2014). Sensitivity and specificity of point-of-care rapid combination syphilis-HIV-HCV tests. PloS One, 9(11), e112190. doi:10.1371/journal.pone.0112190

United States Food and Drug Administration. (2016). FDA Investigated Multistate Outbreak of E. coli O157 Infections Linked to Alfalfa Sprouts From Jack and the Green Sprouts. Retrieved from https://www.fda.gov/food/outbreaks-foodborne-illness/fda-investigated-multistate-outbreak-e-coli-o157-infections-linked-alfalfa-sprouts-jack-and-green

Zeng, D., Chen, Z., Jiang, Y., Xue, F., & Li, B. (2016). Advances and challenges in viability detection of foodborne pathogens. Frontiers in Microbiology, 7, 1833. doi:10.3389/fmicb.2016.01833

For the SLP

While the assignment may be based on a real case, the questions can refer to any outbreak that involved sprouts and E. coli 0157:H7. Knowing the specific pathogen (its characteristics, transmission) and the specific food, how could the contamination have occurred? You are asked to think about a possible point of contamination and about measures of control. Here is another potentially useful reference:

World Health Organization (2011). Enterohaemorrhagic Escherichia coli (EHEC). Retrieved May 22, 2012, from http://www.who.int/mediacenter/factsheets/fs125/en/

Optional Reading

Gray, R. H., Makumbi, F., Serwadda, D., Lutalo, T., Nalugoda, F., Opendi, P., Kigozi, G., … Wawer, M. J. (2007, July 28). Limitations of rapid HIV-1 tests during screening for trials in Uganda: Diagnostic test accuracy study. BMJ, 335(7612), 188. Retrieved on May 22, 2012, from http://www.ncbi.nlm.nih.gov/pubmed/17545184

Masiira, B., Nakiire, L., Kihembo, C., Katushabe, E., Natseri, N., Nabukenya, I., Komakech, I., Makumbi, I., Charles, O., Adatu, F. & Nsubuga, P. (2019). Evaluation of integrated disease surveillance and response (IDSR) core and support functions after the revitalization of IDSR in Uganda from 2012 to 2016. BMC Public Health, 19(1), 46. doi:10.1186/s12889-018-6336-2.