of aids, the course of the disease was closely followed by monitoring the composition of patient blood samples, even though the outcome would not offer the patient any further treatment options. in part, these studies on the appearance of hiv in specific communities permitted the advancement of hypotheses as to the route of transmission of the virus. by understanding how the disease was transmitted, resources could be targeted to the communities at greatest risk in campaigns aimed at reducing the number of new infections. the specific serological diagnostic identification, and later genotypic or molecular identification, of hiv also enabled the development of hypotheses as to the temporal and geographical origins of the virus, as well as a myriad of other hypothesis. the development of molecular diagnostic tools have enabled physicians and researchers to monitor the efficacy of treatment with anti-retroviral drugs. molecular diagnostics are now commonly used to identify hiv in healthy people long before the onset of illness and have been used to demonstrate the existence of people who are genetically resistant to hiv infection. thus, while there still is no cure for aids, there is great therapeutic and predictive benefit to identifying the virus and monitoring the virus levels within the blood of infected individuals, both for the patient and for the community at large. subclinical versus clinical (latent versus apparent) symptomatic infections are apparent and clinical, whereas an infection that is active but does not produce noticeable symptoms may be called inapparent, silent, subclinical, or occult. an infection that is inactive or dormant is called a latent infection. an example of a latent bacterial infection is latent tuberculosis. some viral infections can also be latent, examples of latent viral infections are any of those from the herpesviridae family. the word infection can denote any presence of a particular pathogen at all (no matter how little) but also is often used in a sense implying a clinically apparent infection (in other words, a case of infectious disease). this fact occasionally creates some ambiguity or prompts some usage discussion; to get around this it is common for health professionals to speak of colonization (rather than infection) when they mean that some of the pathogens are present but that no clinically apparent infection (no disease) is present. course of infection different terms are used to describe how and where infections present over time. in an acute infection, symptoms develop rapidly; its course can either be rapid or protracted. in chronic infection, symptoms usually develop gradually over weeks or months and are slow to resolve. in subacute infections, symptoms take longer to develop than in acute infections but arise more quickly than those of chronic infections. a focal infection is an initial site of infection from which organisms travel via the bloodstream to another area of the body. primary versus opportunistic