Outcome Of Infectious Diseases

Given the complexities of host defenses and microbial virulence, it is not surprising that the factors determining outcome between these two living entities are also complicated. Basically, outcome depends on the state of the host's health, the virulence of the pathogen, and whether the host can clear the pathogen before infection and disease cause irreparable harm or death (Figure 3-11).

The time for a disease or infection to develop also depends on host and microbial factors. Infectious processes that develop quickly are referred to as acute infections, and those that develop and progress slowly, sometimes over a period of years, are known as chronic infections. Some pathogens, particularly certain viruses, can be clinically silent inside the body without any noticeable effect on the host before suddenly causing a severe and acute infection. During the silent phase, the infection is said to be latent. Again, depending on host and microbial factors, acute, chronic, or latent infections can result in any of the outcomes detailed in Figure 3-11.

Medical intervention can help the host fight the infection but usually is not instituted until after the host is aware that an infectious process is underway. The clues that an infection is occurring are known as the signs and symptoms of disease and result from host responses (e.g., inflammatory and immune responses) to the action of microbial virulence factors (Box 3-10). The signs and symptoms reflect the stages of infection. In turn, the stages of infection generally reflect the stages in host-microorganism interactions (Figure 3-12).

Whether medical procedures contribute to controlling or clearing an infection depends on key factors, including:

  • The severity of the infection, which is determined by host and microbial interactions already discussed
  • Accuracy in diagnosing the pathogens or pathogens causing the infection, which is the primary function of diagnostic microbiology
  • Whether the patient receives appropriate treatment for the infection (which heavily depends on accurate diagnosis)

Figure 3-12 Host-microorganism interactions and stages of infection or disease.

Host-microorganism Intel

Encounter and entry

Colonization and entry

Invasion and dissemination


Pathogen encounters and colonizes host surface

Pathogen multiplies and breaches host surface defenses

Pathogen invades deeper tissues and disseminates, encounters inflammatory and immune responses

Pathogen completes cycle:

  • Leaves host
  • Destroys host
  • Remains In latent state
  • Is destroyed by host

Incubation stage

No signs or symptoms

Prodromal stage

First signs and symptoms, pathogen may be highly communicable

Clinical stage

Peak of characteristic signs and symptoms of infection or disease

Stage of decline

Condition of host deteriorates possibly to death or signs and symptoms begin to subside as host condition improves

Convalescent stage

Full recovery of surviving host or chronic infection develops, or death

BOX 3-10 Signs and Symptoms of Infection and Infectious Diseases

General or localized aches and pains



Swollen lymph nodes Rashes

Redness and swelling Cough and sneezes

Congestion of nasal and anus passages Sore throat Nausea and vomiting Diarrhea

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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