To help prevent the spread of disease among school children, the CDC has developed guidelines based on the risk of transmission during the course of the disease. On the other hand, cold-causing rhinoviruses are somewhat fragile, typically surviving less than a day outside of physiological fluids.ДЄ human acting as a reservoir of a pathogen may or may not be capable of transmitting the pathogen, depending on the stage of infection and the pathogen. For example, a study that looked at the ability of influenza viruses to infect a cell culture after varying amounts of time on a banknote showed survival times from 48 hours to 17 days, depending on how they were deposited on the banknote. Although many viruses are soon destroyed once in contact with air, water, or other non-physiological conditions, certain types are capable of persisting outside of a living cell for varying amounts of time. For example, Clostridium tetani survives in the soil and in the presence of oxygen as a resistant endospore. Pathogens may have mechanisms of dormancy or resilience that allow them to survive (but typically not to reproduce) for varying periods of time in nonliving environments. These environments may also become contaminated with pathogens in human feces, pathogens shed by intermediate hosts, or pathogens contained in the remains of intermediate hosts. These may naturally harbor the organism because it may grow in that environment. Nonliving reservoirs can include soil and water in the environment. Reservoirs can be living organisms or nonliving sites. Reservoirs and CarriersДЇor pathogens to persist over long periods of time they require reservoir s where they normally reside. This section will explore where pathogens survive-both inside and outside hosts-and some of the many ways they move from one host to another. Hosts have evolved defenses against pathogens, but because their rates of evolution are typically slower than their pathogens (because their generation times are longer), hosts are usually at an evolutionary disadvantage. Pathogens often have elaborate adaptations to exploit host biology, behavior, and ecology to live in and move between hosts. But having infected one host, all pathogens must also have a mechanism of transfer from one host to another or they will die when their host dies. Many pathogens require a living host to survive, while others may be able to persist in a dormant state outside of a living host. Understanding how infectious pathogens spread is critical to preventing infectious disease.

Explain the prevalence of nosocomial infections.

Compare contact, vector, and vehicle modes of transmission.

Describe the different types of disease reservoirs.

Define transmit