Some of these illnesses have unique features which make them particularly difficult to track as subjects of surveillance. For example, Lyme tests are often unreliable. Also, "many viruses and bacteria cause nonspecific syndromes or symptom complexes that include most diarrheal and respiratory symptoms" (Ritz, Tager, & Balms 2005). This is also true of tracking the efficacy of treatments: "in cases where there are long delays between the implementation of an intervention and the reduction in disease incidence or morbidity, it may be difficult to quantitate precisely (or even accurately) the extent to which the intervention altered the outcome of the disease" (Ritz, Tager, & Balms 2005). This is particularly manifest in treatments which are multifaceted and are taken over time (like AIDS 'drug cocktails') or require environmental controls to be effective (like preventing malaria or other mosquito-borne illnesses).
However, despite the innate challenges in tracking diseases, a number of new trends have emerged to enhance the capacity of government agencies to do so. One is through technology: a recent study of patterns of Google searches for influenza-like illness, gastroenteritis, and chickenpox found that "one well-chosen...
This strong correlation is important given that these particular diseases are often not treated by medical professionals and thus may go 'under the radar' of detection as the patient recuperates and self-treats at home. Internet search engine use can thus be a powerful way to remedy some of the problems of underreporting of specific illnesses.
References
Historical perspectives notifiable disease surveillance and notifiable disease statistics -- United
States, June 1946 and June 1996. (1996). MMWR, 45(25); 530-536. Retrieved:
http://www.cdc.gov/mmwr/preview/mmwrhtml/00042744.htm
Pelat, C. (2009). More diseases tracked using Google trends. Emerging Infectious Disease
Journal 15 (8). Retrieved:
http://wwwnc.cdc.gov/eid/article/15/8/09-0299_article.htm
Ritz, B., Tager, I, & Balmes, J. (2005). Can lessons from public health disease surveillance be applied to environmental public health tracking? Environmental Health
Perspective, 113(3):243-249. Retrieved:
http://www.medscape.com/viewarticle/501081_2
