Lesson 5: Public Health Surveillance

Appendix E. Limitations of Notifiable Disease Surveillance and Recommendations for Improvement

Surveillance need not be perfect to be useful. However, surveillance might have limitations, particularly as a result of underreporting, lack of representativeness, and lack of timeliness, that compromise its usefulness. Fortunately, health departments can implement measures to overcome these hurdles.

Although the intention of the laws and regulations of each state in the United States is that every case of a notifiable disease be reported, the reality is otherwise. For rare, serious diseases of public health importance (e.g., rabies, plague, or botulism), the percentage of cases actually reported might approach 100% of diagnosed cases. Reporting completeness for diseases that have local programs that specifically look for cases of the disease to aid in their prevention or control (e.g., AIDS, tuberculosis, and sexually transmitted diseases [STDs]) has been identified as being higher than for other, nonlife-threatening diseases.(35) For other diseases, reporting has been reported to be as low as 9%.(35 Table 5.8 illustrates this situation for the identification and reporting of shigellosis. The authors of the study from which these data are derived concluded that the number of Shigella cases reported nationally should be multiplied by 20 to obtain a more realistic estimate of the actual number of infections.(36) Others have proposed multiplication factors of 38 for infectious agents that cause nonbloody diarrhea, 20 for agents that cause bloody diarrhea, and two for pathogens that typically cause severe gastrointestinal illness.(37)

Limitations

Underreporting. For the majority of notifiable diseases, data for surveillance are based on passive reporting by physicians and other health-care providers. Studies have demonstrated that in the majority of jurisdictions, only a fraction of cases of the notifiable diseases overall are ever reported.(37–39) The most obvious result of such underreporting is that effective action is delayed, and cases occur that might have been prevented by prompt reporting and prompt initiation of control measures. For example, if a case of hepatitis A in a food handler goes unreported, the opportunity to provide protective immune globulin to restaurant patrons will be missed, and cases or an outbreak of hepatitis A that should have been prevented will instead occur. However, underreported data might still be useful for assessing trends or other patterns reflecting the occurrence or burden of disease.

Health-care providers cite a number of reasons for not reporting.(40) Selected reasons are listed in the following text. Public health agencies must recognize these barriers to reporting, because the majority are within an agency's power to address or correct.

Lack of representativeness of reported cases. Underreporting is not uniform or random. Two important biases distort the completeness of reporting. First, health-care providers are more likely to report a case that results in severe illness and hospitalization than a mild case, even though a person with mild illness might be more likely to transmit infection to others because the person might not be confined at home or in the hospital. This bias results in an inflated estimate of disease severity in such measures as the death-to-case ratio. Second, health-care providers are more likely to report cases when the disease is receiving media attention. This bias results in an underestimate of the baseline incidence of disease after media attention wanes.

Both biases were operating in 1981 during the national epidemic of tampon-associated toxic shock syndrome. Early reports indicated a death-to-case ratio much higher than the ratio determined by subsequent studies, and reported cases declined more than incident cases after the publicity waned.(41)

Lack of timeliness. Lack of timeliness can occur at almost any step in the collection, analysis, and dissemination of data on notifiable diseases. The reasons for the delays vary. Certain delays are disease-dependent. For example, physicians cannot diagnose certain diseases until confirmatory laboratory and other tests have been completed. Certain delays are caused by cumbersome or inefficient reporting procedures. Delays in analysis are common when surveillance is believed to be a rote function rather than as one that provides information for action. Finally, delays at any step might culminate in delays in dissemination, with the result that the medical and public health communities do not have the information they need to take prompt action.

Recommendations for Improving Notifiable Disease Surveillance

The preceding limitations of reporting systems demonstrate multiple steps that can be taken by a local or state health department to improve reporting.

Improving awareness of practitioners. Most important, all persons who have a responsibility to report must be aware of this responsibility. The health department should actively publicize the list of notifiable diseases and the reporting mechanisms. Certain states send the reporting requirements in a packet when a physician becomes licensed to practice in the state. Other state health officials visit hospitals and speak at medical presentations or seminars to increase the visibility of surveillance.

Incentives. Health-care providers might need services or therapeutic agents that are only available from the health department, which might be able to use this need to obtain reports of certain diseases. Services can include laboratory testing and consultation on diagnosis and treatment of certain diseases. Agents might include immune globulin for human rabies and hepatitis B and antitoxin for diphtheria and botulism. These services and agents might be particularly effective incentives if they are available promptly and delivered in a professional, authoritative manner.(10)

Simplify reporting. Reporting should be as simple as possible. Health departments often accept telephone reports or have toll-free telephone numbers. If paper forms are used, they should be widely available and easy to complete, and they should ask only for relevant information. Certain state health departments have arranged for electronic transfer of laboratory or other patient- or case-related data; therefore, reporting is accomplished automatically at scheduled times or at the push of a computer key.

Frequent feedback. The role of feedback cannot be overemphasized. Feedback can be written (e.g., a monthly newsletter) or oral (e.g., updates at regular meetings of medical staff or at rounds). The feedback should be timely, informative, interesting, and relevant to each reporter's practice. Feedback should include information about disease patterns and control activities to increase awareness and to reinforce the importance of participating in a meaningful public health activity.

Widening the net. Traditionally, surveillance for notifiable diseases has relied on reporting by physicians. Almost every state now requires reporting of positive cultures or diagnostic tests for notifiable diseases by commercial and hospital laboratories. For certain states, the number of laboratory reports exceeds the number of reports from physicians, hospitals, clinics, and other sources. Other health-care staff (e.g., infection control personnel and school nurses) can be used as sources of data for surveillance. Another way to widen the net is to develop alternative methods for conducting surveillance (e.g., using secondary sources of data). This method has been used effectively for surveillance of influenza and certain injuries.

Shifting the burden. Another effective approach is to shift the burden for gathering data from the health-care provider to the health department. In essence, this approach involves ongoing surveys of providers to more completely identify cases of disease, and it has been demonstrated to increase the number of cases and the proportion of identified-to-incident cases. Because health department staff contact health-care providers regularly, this approach also promotes closer personal ties among providers and health department staff. As with surveys in general, this approach is relatively expensive, and its cost-effectiveness is not entirely clear. In practice, it is usually limited to disease elimination programs, short-term intensive investigation and control activities, or seasonal problems (e.g., certain arboviral diseases).

References (This Section)

10. Hopkins RS. Design and operation of state and local infectious disease surveillance systems. J Public Health Management Practice 2005;11(3):184—90.

35. Doyle TJ, Glynn MK, Groseclose SL. Completeness of notifiable infectious disease reporting in the United States: an analytic literature review. Am J Epidemiol 2002;155:866–74.
36. Rosenberg MJ, Marr JS, Gangarosa EJ, Pollard RA, Wallace M, Brolnitsky O. Shigella surveillance in the United States, 1975. J Infect Dis 1977;136:458–60.
37. Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in the United States. Emerg Infect Dis 1999;5:607–25.
38. Campos-Outcalt D, England R, Porter B. Reporting of communicable diseases by university physicians. Public Health Rep 1991;106:579–83.
39. Marier R. The reporting of communicable diseases. Am J Epidemiol 1977;105:587–90.
40. Konowitz PM, Petrossian GA, Rose DN. The underreporting of disease and physicians' knowledge of reporting requirements. Public Health Rep 1984;99:31–5.
41. Hajjeh R, Reingold A, Weil A, Shutt K, Schuchat A, Perkins BA. Toxic shock syndrome in the United States: surveillance update, 1979–1996. Emerg Infect Dis 1999;5:807–10.