Module 4: Screening and Diagnostics in Developing Countries

The Importance of Screening and Diagnostics in Public Health Surveillance

The success of surveillance systems depends on the accurate identification and diagnosis of health conditions; in order for a case to be counted by a surveillance system, it first must be diagnosed. Public health surveillance in developing countries could be dramatically improved with increased access to quality screening and diagnostic tests.(1) Outcomes resulting from these conditions would improve with earlier detection, especially for conditions that do not cause specific, recognizable symptoms. In developing countries where resources are limited, spending on diagnostics is often inadequate. The WHO found that in a hospital in Malawi, only 6% of health funds were spent on diagnostics.(2)

Types of Tests and Their Application in Developing Countries

Microscopy is used to identify pathogens in samples taken from patients in the field. Though diagnosing with microscopy is effective, it is not always available in developing countries that lack access to a laboratory or an educated scientist—both of which are needed to identify pathogens with a microscope.(3)

Culture(when cells are grown in controlled conditions) is a common way that diagnosis occurs in the developed world. There is a variety of problems with culture in the developing world, however. One is that growing cells takes significant time, so test results can take weeks to return from the laboratory. This is not suitable for an environment in which people may be traveling long distances to health clinics and cannot afford a return trip to view the results of their tests.(4) Currently a Tuberculosis culture from patient specimens is a problem in the developing world because Tuberculosis is a very slow-growing bacterium. Culture also requires supplies of reagents, electricity, special transportation of samples from the field, and educated personnel.(5) These necessities for culture diagnostics are often unavailable in developing countries.

Antibody or Antigen detection tests are thought of as better suited for the conditions of the developing world than are culture tests. They only require simple equipment and do not need special transportation. They are also less expensive to make, and their results can be available in a matter of hours.(6)

Nucleic Acid Amplification Technology (NAAT) tests are highly sensitive and specific tests that facilitate cost effective public health interventions. They have a high potential for application in the developing world because they can generate a test result from urine and other specimens that can be gathered in minimally invasive ways.(7) However, NAAT tests need special equipment and educated personnel to conduct them, which are often unavailable in low-income countries.(8)

Point of care tests (POC) are thought of as the most applicable type of tests in developing countries. These tests usually work by detecting antibodies that fight particular pathogens. They are relatively inexpensive, but give fast results, and are easy to conduct.(9) The problem with POC tests in the developing world is that they are of varying reliability in the field, and also have not been developed and tested enough to be deemed cost effective for many major diseases. POC tests are currently available for some diseases, however, including malaria (pictured below), syphilis, and HIV.(10)  
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The Need for the Development of New Tests

Research and development of new diagnostic tests for illnesses that disproportionately affect developing countries are highly dependent on donations from private sources (e.g. the Bill and Melinda Gates Foundation or pharmaceutical companies).(11) Major players need to be better educated on the importance of diagnostic tests in the global fight against disease. In some cases, new diagnostic test development may be more cost-effective than the development of new drugs.(12) Diseases need to be assessed to determine whether resource allocation to develop better diagnostic screening tests is appropriate.

The WHO has created a list of criteria by which diseases should be assessed in deciding if a new diagnostic test should be developed.(13) They are:

New diagnostic tests should be developed with the challenges of a developing country in mind. The Sexually Transmitted Disease Diagnostics Initiative calls the ideal diagnostic test an ASSURED test.(14) ASSURED is an acronym that describes the most valuable diagnostic test characteristics:

Which Diseases Need New Diagnostics in Developing Countries

According to an article by two scientists in the London School of Hygiene and Tropical Medicine,(15) the development of a few specific POC tests would have a tremendous effect on public health initiatives in the developing world. Peeling and Mabey call for the development of the following POC tests to be the highest priority:(16)

The following are barriers that exist in developing countries to developing appropriate diagnostic tests:(17)

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Footnotes

(1) Mabey, D., Peeling, R. W., Ustianowski, A., & Perkins, M. D. (2004, March). Diagnostics for the Developing World. Retrieved May 18, 2012, from Nature Reviews: Microbiology.

(2) Peeling, R. W., & Mabey, D. (2010, July 23). Point-of-care tests for diagnosing infections in the developing world. Retrieved May 30, 2012, from Clinical Microbiology and Infection.

(3) Mabey, D., Peeling, R. W., Ustianowski, A., & Perkins, M. D. (2004, March). Diagnostics for the Developing World. Retrieved May 18, 2012, from Nature Reviews: Microbiology.

(4) Ibid.

(5) Ibid.

(6) Ibid.

(7) Ibid.

(8) Ibid.

(9)Point-of-Care Testing. (n.d.). Retrieved May 18, 2012, from American Association for Clinical Chemistry.

(10) Mabey, D., Peeling, R. W., Ustianowski, A., & Perkins, M. D. (2004, March). Diagnostics for the Developing World. Retrieved May 18, 2012, from Nature Reviews: Microbiology.

(11) Ibid.

(12) Ibid.

(13) Ibid.

(14)SDI: Priorities. (2001, January). Retrieved May 29, 2012, from Sexually Transmitted Diseases Diagnostic Initiative.

(15) Peeling, R. W., & Mabey, D. (2010, July 23). Point-of-care tests for diagnosing infections in the developing world. Retrieved May 30, 2012, from Clinical Microbiology and Infection.

(16) Ibid.

(17) Ibid.

(18) Ibid.