Editing Infection Control and Safety (section)

== Stages and Types of Infection ==

; Incubation period
: From exposure to the first symptoms. The person may be contagious during this period even while feeling well.
; Prodromal stage
: Vague, nonspecific symptoms such as malaise and low-grade fever. Communicability is often highest here.
; Illness (acute) stage
: Signs and symptoms specific to the infection are present.
; Convalescent stage
: Symptoms resolve and the host recovers. Recovery may be incomplete if tissue damage occurred.

Infections may be '''localized''' (redness, warmth, swelling, pain, purulent drainage at one site) or '''systemic''' (fever, chills, tachycardia, tachypnea, leukocytosis, malaise, and in severe cases hypotension and organ dysfunction). '''Latent''' infections, such as latent tuberculosis or herpes viruses, persist without symptoms and may reactivate.

'''Application note for older adults.''' Older adults and immunosuppressed patients may not mount a fever. New-onset confusion, falls, decreased appetite, incontinence, lethargy, or a small drop in blood pressure may be the only sign of infection. Do not rule out infection because the temperature is normal.

'''Laboratory clues.''' An elevated white blood cell count with a rise in immature neutrophils (bands), sometimes called a left shift, suggests acute bacterial infection. Elevated lymphocytes suggest a viral process. Elevated eosinophils suggest parasitic infection or allergy. A rising C-reactive protein or procalcitonin supports bacterial inflammation. Neutropenia, generally an absolute neutrophil count below 1,500 cells per microliter and severe below 500, greatly raises infection risk while blunting the usual signs. In a neutropenic patient, fever is an emergency: obtain cultures and give the ordered broad-spectrum antibiotic without delay.