infection
(in-fek'shŏn 
)
[L. infectio, discoloration, dye]
A disease caused by microorganisms, esp. those that release toxins or invade body tissues. Worldwide, infectious diseases such as malaria, tuberculosis, hepatitis viruses, and diarrheal illnesses produce more disability and death than any other cause. Infection differs from colonization of the body by microorganisms in that during colonization, microbes reside harmlessly in the body or perform useful functions for it, e.g., bacteria in the gut that produce vitamin K. By contrast, infectious illnesses typically cause bodily harm.
Etiology: The most common pathogenic organisms are bacteria (including mycobacteria, Escherichia coli, mycoplasmas, spirochetes, chlamydiae, and rickettsiae), viruses, fungi, protozoa, and helminths. Life-threatening infectious disease usually occurs when immunity is weak or suppressed (as during the first few months of life; in older or malnourished persons; in trauma or burn victims; in leukopenic patients; and in those with chronic illnesses such as diabetes mellitus, renal failure, cancer, asplenia, alcoholism, or heart, lung, or liver disease). Many disease-causing agents, however, may afflict vigorous people, young or old, fit or weak. Some examples include sexually transmitted illnesses (such as herpes simplex or chlamydiosis), respiratory illnesses (influenza or varicella), and food or waterborne pathogens (cholera, schistosomiasis).
Symptoms: Systemic infections cause fevers, chills, sweats, malaise, and occasionally, headache, muscle and joint pains, or changes in mental status. Localized infections produce tissue redness, swelling, tenderness, heat, and loss of function.
Transmission: Pathogens can be transmitted to their hosts by many mechanisms: inhalation, ingestion, injection or the bite of a vector, direct (skin-to-skin) contact, contact with blood or body fluids, fetomaternal contact, contact with contaminated articles (fomites), or self-inoculation.
In health care settings, infections are often transmitted to patients by the hand s of professional staff or other employees. Hand hygiene before and after patient contact prevents many of these infections.
Defenses: The body's defenses against infection begin with mechanisms that block entry of the organism into the skin or the respiratory, gastrointestinal, or genitourinary tract. These defenses include chemicals, e.g., lysozymes in tears, fatty acids in skin, gastric acid, and pancreatic enzymes in the bowel; mucus that traps the organism; clusters of antibody-producing B lymphocytes, e.g., tonsils, Peyer patches; and bacteria and fungi (normal flora) on the skin and mucosal surfaces that destroy more dangerous organisms. In patients receiving immunosuppressive drug therapy, the normal flora can become the source of opportunistic infections. Also, one organism can impair external defenses and permit another to enter; e.g., viruses can enhance bacterial invasion by damaging respiratory tract mucosa.
The body's second line of defense is inflammation, the nonspecific immune response. The third major defensive system, the specific immune response, depends on lymphocyte activation, during which B and T cells recognize specific antigenic markers on the organism. B cells produce immunoglobulins (antibodies), and T cells orchestrate a multifaceted attack by cytotoxic cells.
SEE: B cell ; T cell ; inflammation for table.
Spread: Once pathogens have crossed cutaneous or mucosal barriers and gained entry into internal tissues, they may spread quickly along membranes such as the meninges, pleura, or peritoneum. Some pathogens produce enzymes that damage cell membranes, enabling them to move rapidly from cell to cell. Others enter the lymphatic channels; if they can overcome white blood cell defenses in the lymph nodes, they move into the bloodstream to multiply at other sites. This is frequently seen with pyogenic organisms, which create abscesses far from the initial entry site. Viruses or rickettsiae, which reproduce only inside cells, travel in the blood to cause systemic infections; viruses that damage a fetus during pregnancy (such as rubella and cytomegalovirus) travel via the blood.
Diagnosis: Although many infections (such as those that cause characteristic rashes) are diagnosed clinically, definitive identification of infection usually occurs in the laboratory. Carefully collected and cultured specimens of blood, urine, stool, sputum, or other body fluids are used to identify pathogens and their susceptibilities to treatment.
Treatment: Many infections, like the common cold, are self-limited and require no specific treatment. Understand ing this concept is crucial because the misuse of antibiotics does not help the affected patient and may damage society by fostering antimicrobial resistance, e.g., in microorganisms such as methicillin-resistant Staphylococcus aureus. Many common infections, such as urinary tract infections or impetigo, respond well to antimicrobial drugs. Others, like abscesses, may require incision and drainage.
acute i.An infection that appears suddenly and may last a long or short time.
acute HIV i.The period of initial infection with HIV when the virus first replicates, often causing a flulike or mononucleosis-like syndrome, and typically lasting for 2 to 4 weeks.
Acutely infected patients may be difficult to diagnose because the signs and symptoms of acute HIV infection resemble other illnesses. These patients nonetheless carry a large burden of circulating virus in their plasma and are highly infectious.
SYN: acute retroviral syndrome.airborne i.An infection caused by the inhalation of disease-causing microorganisms.
apical i.An infection at the tip of the root of a tooth.
autochthonous i.Infection caused by organisms normally present in the body. It may occur when host defenses are compromised, or when resident flora are introduced into an abnormal site.
bacterial i.Any disease caused by bacteria. Bacteria exist in a variety of relationships with the human body. They colonize body surfaces and provide benefits, as by limiting the growth of pathogens and by producing vitamins for absorption (in a symbiotic relationship). Bacteria can coexist with the human body without producing harmful or beneficial effects (in a commensal relationship). Bacteria may also invade tissues, damage cells, trigger systemic inflammatory responses, and release toxins (in a pathogenic or infectious relationship).
SEE: bacterium for table.
SEE: urinary tract infection .
blood-borne i.An infection transmitted through contact with the blood (cells, serum, or plasma) of an infected person. The contact may occur sexually, through injection, or via a medical or dental procedure in which a blood-contaminated instrument is inadvertently used after inadequate sterilization. Examples of blood-borne infections include hepatitis B and C and AIDS.
SEE: needle-stick injury .
ABBR: BSI
A general term for bacteremia, fungemia, parasitemia, and /or viremia.breakthrough i.An infection that occurs despite previous vaccination.
chronic i.An infection having a protracted course.
concurrent i.The existence of two or more infections at the same time.
SEE: superinfection.
cross i.The transfer of an infectious organism or disease from one patient in a hospital to another.
cryptogenic i.An infection whose source is unknown.
ABBR: CMV infection
A persistent, latent infection of white blood cells caused by cytomegalovirus (CMV). Approx. 60% of people over 35 have been infected with CMV, usually during childhood or early adulthood; the incidence appears to be higher in those of low socioeconomic status. Primary infection is usually mild in people with normal immune function, but CMV can be reactivated and cause overt disease in pregnant women, AIDS patients, or those receiving immunosuppressive therapy following organ transplantation. CMV has been isolated from saliva, urine, semen, breast milk, feces, blood, and vaginal secretions of those infected; it is usually transmitted through contact with infected secretions that retain the virus for months to years.During pregnancy, the woman can transmit the virus transplacentally to the fetus with devastating results. Approx. 10% of infected infants develop CMV inclusion disease, marked by anemia, thrombocytopenia, purpura, hepatosplenomegaly, microcephaly, and abnormal mental or motor development; more than 50% of these infants die. Most fetal infections occur when the mother is infected with CMV for the first time during this pregnancy, but they may also occur following reinfection or reactivation of the virus. Patients with AIDS or organ transplants may develop disseminated infection that causes retinitis, esophagitis, colitis, meningoencephalitis, pneumonitis, and inflammation of the renal tubules.
CMV is transmitted from person to person by sexual activity, during pregnancy or delivery, during organ transplantation, or by contaminated secretions or, occasionally, by blood transfusions. Health care workers caring for infected newborns or the immunosuppressed are at no greater risk for acquiring CMV infection than are those who care for other groups of patients (approx. 3%). Pregnant women and all health care workers should strictly adhere to stand ard infection control precautions.
Primary infection in the healthy is usually asymptomatic, but some people develop mononucleosis-type symptoms (fever, sore throat, swollen gland s). Symptoms in immunosuppressed patients are related to the organ system infected by CMV and include blurred vision progressing to blindness; severe diarrhea; and cough, dyspnea, and hypoxemia. Antibodies seen in the blood identify infection but do not protect against reactivation of the virus.
Antiviral agents such as ganciclovir and foscarnet are used to treat retinitis, colitis, and pneumonitis in immunosuppressed patients; chronic antiviral therapy has been used to suppress CMV, but this protocol has not been effective in preventing recurrence of CMV or development of meningoencephalitis. Ganciclovir has limited effect in congenital CMV. No vaccine is available.
Health care providers can help prevent CMV infections by advising pregnant women and the immunocompromised to avoid exposure to contact with people who have confirmed and or suspected cases of CMV. The virus spreads from one person to another as a result of exposure to blood (as in transfusions) and other body fluids including feces, urine, and saliva. Contact with the diapers or drool of an infected child may result in infection of a person who has previously been unexposed to the infection. CMV is the most common congenital infection, affecting about 35,000 newborns each year. CMV infection that is newly acquired during the first trimester of pregnancy can be very hazardous to the developing fetus; therefore, young women who have no antibodies to CMV should avoid providing child care to infected youngsters. In the U.S., nurses who have failed to advise infected patients of the risk that CMV may pose to others have been judged to be negligent by the courts. Parents of children with severe congenital CMV require support and counseling. Although CMV infection in most nonpregnant adults is not harmful, it can cause serious illnesses or death in those with HIV/AIDS, organ transplants, and those who take immunosuppressive or cancer chemotherapeutic drugs. Infected immunosuppressed patients with CMV should be advised about the uses of prescribed drug therapies, the importance of completing the full course of therapy, and adverse effects to report for help in managing them. Family caregivers for the infected should be taught to observe stand ard precautions when hand ling body secretions. Since asymptomatic people may have the virus and secrete it, stand ard precautions should be maintained by health care professionals at all times when such secretions are present or being hand led.
deep neck i.An infection that enters the fascial planes of the neck after originating in the oral cavity, pharynx, or a regional lymph node. It may be life-threatening if the infection enters the carotid sheath, the paravertebral spaces, or the mediastinum. Death may also result from sepsis, asphyxiation, or hemorrhage. Aggressive surgical therapy is usually required because antibiotics alone infrequently control the disease.
diabetic foot i.A polymicrobial infection of the bones and soft tissues of the lower extremities of patients with diabetes mellitus, typically those patients who have vascular insufficiency or neuropathic foot disease. Eradication of the infection may require prolonged courses of antibiotics, surgical débridement or amputation, or reconstruction or bypass of occluded arteries.
SEE: diabetic foot ulcer ; SEE: illus..
ABBR: DGI
SEE: gonococcal arthritis .
droplet i.An infection acquired by the inhalation of a microorganism in the air, esp. one added to the air by sneezing or coughing.
focal i.Infection occurring near a focus, such as the cavity of a tooth.
fungal i.Pathological invasion of the body by yeast or other fungi. Fungi are most likely to produce disease in patients whose immune defenses are compromised.
SEE: table - Fungal Infections.
fungal i. of nail Infection of a nail by one of a number of fungi. Systemic therapy with antifungal drugs may eradicate the infection.
ABBR: HAI
Nosocomial infection.hospital-acquired i.Nosocomial infection.
hospital-onset i.Nosocomial infection.
inapparent i.An infection that is asymptomatic or undetected.
local i.An infection that has not spread but remains contained near the entry site.
low-density i.An infection in which a relatively small number of organisms is present in the body, e.g., its fluids or organs. Such infections often elude diagnosis.
low-grade i.An imprecise term for a subacute or chronic infection with only mild inflammation and without pus formation.
nosocomial i.An infection acquired in a hospital, nursing home, or other health care setting. Patients in burn units and surgical intensive care units have the highest rates of nosocomial infections. SYN: health-care associated infection; hospital-acquired infection; hospital-onset infection.
Hospital-acquired infections result from the exposure of debilitated patients to the drug-altered environment of the hospital, where indwelling urinary catheters, intravenous lines, and endotracheal tubes enter normally sterile body sites and allow microbes to penetrate and multiply. Over 2 million nosocomial infections occur in the U.S. annually. Antibiotic-resistant organisms such as Enterobacter spp., Pseudomonas spp., staphylococci, enterococci, Clostridium difficile, and fungi often are responsible for the infectious outbreaks that result. Stand ard precautions and infection control procedures limit the incidence of nosocomial infections.
ABBR: OI
1Any infection that results from a defective immune system that cannot defend against pathogens normally found in the environment. Common types include bacterial (Pseudomonas aeruginosa), fungal (Cand ida albicans), protozoan (Pneumocystis jirovecii), and viral (cytomegalovirus). Opportunistic infections are seen in patients with impaired defenses against disease, such as those with cystic fibrosis, poorly controlled diabetes mellitus, acquired or congenital immune deficiencies, or organ transplants.2An infection that results when resident flora proliferate and infect a body site in which they are normally present or at some other location. In healthy humans, the millions of bacteria in and on the body do not cause infection or disease. Host defenses and interaction with other microorganisms prevent excess growth of potential pathogens. A great number of factors, many poorly understood, may allow a normal bacterial resident to proliferate and cause disease.pocket i.Infection of the tissues beneath the skin into which an implanted device, such as a pacemaker or defibrillator, has been surgically inserted.
protozoal i.An infection with a protozoon, e.g., malaria.
pyogenic i.An infection resulting from pus-forming organisms.
ABBR: RTI
Any infection of the reproductive organs. The most common causes are sexually transmitted diseases, but infections may also result from bacterial overgrowth or occasionally when instruments used in medical procedures introduce microorganisms. In women, RTIs can cause pelvic pain, subfertility, infertility, or damage to the developing fetus. RTIs in men include epididymitis, prostatitis, and urethritis.secondary i.An infection made possible by a primary infection that lowers the host's resistance, e.g., bacterial pneumonia following influenza.
sexually transmitted i.Sexually transmitted disease.
skin and skin-structure i.Any infection affecting the epidermis or subcutaneous tissue. Common signs and symptoms include redness, swelling, induration, localized warmth, purulent drainage, and tenderness to palpation.
slow virus i.An infection caused by a virus that remains dormant in the body for a prolonged period before causing signs and symptoms of illness. Such viruses may require years to incubate before causing diseases. Examples include progressive multifocal leukoencephalopathy and subacute sclerosing panencephalitis.
spillover i.Spread of an infection from one host organism to another, typically during an epidemic in the original host. SYN: spillover event.
subacute i.An infection intermediate between acute and chronic.
subclinical i.An infection that is immunologically confirmed but does not produce obvious symptoms or signs.
submicroscopic i.Subpatent infection.
subpatent i.An infection that is not detected by simple diagnostic tests, as with microscopy or rapid diagnostic tests. SYN: submicroscopic infection.
ABBR: SSI
An infection that occurs within 30 days of an operation, either at the suture line, just beneath it, or in internal organs and spaces that were operated upon. SSIs are among the most common health-care associated infections. They are expensive and time-consuming to treat and are fatal in about 3 % of patients. SYN: surgical wound infection .surgical wound i.Surgical site infection.
SEE: illus..
systemic i.An infection in which the infecting agent or organisms circulate throughout the body.
terminal i.An often fatal infection appearing in the late stage of another disease.
transfusion-associated bacterial i.Transfusion-transmitted bacterial infection.
transfusion-transmitted bacterial i.
ABBR: TTBI
Illness in a transfusion recipient that develops after the infusion of contaminated blood or blood products, esp. platelets. It usually results from colonization of the blood product during hand ling or storage or, less frequently, from an unsuspected infection in the blood donor. Coagulase-negative staphylococci are often responsible. Other bacteria that sometimes cause TTBI include Pseudomonas species, Anaplasma, Babesia, and Rickettsia.Viruses may also be transmitted from blood donors to transfusion recipients. They may include cytomegalovirus, encephalitis viruses, and , rarely, hepatitis viruses or HIV.
SYN: transfusion-associated bacterial infection .ABBR: URI
An imprecise term for any infection involving the nasal passages, pharynx or sinuses; the common cold. The cause is usually viral or bacterial, rarely fungal. SYN: upper respiratory tract infection.upper respiratory tract i.Upper respiratory infection
ABBR: UTI
Infection of the kidneys, ureters, or bladder by microorganisms that either ascend from the urethra (95% of cases) or that spread to the kidney from the bloodstream (5%). About 7 million Americans visit health care providers each year because of UTIs. These infections commonly occur in otherwise healthy women, men with prostatic hypertrophy or bladder outlet obstruction, children with congenital anatomical abnormalities of the urinary tract, and patients with urinary stasis related to incomplete bladder emptying, neurogenic bladder, or indwelling bladder catheters.SEE: clean-catch method ; cystitis; pyelonephritis; urethritis.
Escherichia coli causes about 80% of all UTIs. In young women, Staphylococcus saprophyticus is also common. In men with prostate disease, enterococci are often responsible. The small remaining percentage of infections may be caused by Klebsiella species, Proteus mirabilis, Staphylococcus aureus, Pseudomonas aeruginosa, or other virulent organisms.
The presenting symptoms of UTI vary enormously. Young patients with bladder infections may have pain with urination; urinary frequency or urgency, or both; pelvic or suprapubic discomfort; low-grade fevers; or a change in the appearance or odor of their urine (cloudy, malodorous, or rarely bloody). Older patients may present with fever, lethargy, confusion, delirium, or coma caused by urosepsis. Patients with pyelonephritis often complain of flank pain, prostration, nausea, vomiting, diarrhea, and high fevers with shaking chills. UTI may also be asymptomatic, esp. during pregnancy. Asymptomatic UTI during pregnancy is a contributing factor to maternal pyelonephritis or fetal prematurity and stillbirth.
Urinalysis (obtained either as a clean catch or catheterized specimen) and subsequent urinary culture determine the presence of UTI, the suspect microorganism, and the optimal antibiotic therapy. A dipstick test may identify leukocyte esterase and nitrite in a urinary specimen, strongly suggesting a UTI. The presence of more than 8 to 10 white blood cells per high-power field of spun urine also strongly suggests UTI, as does the presence of bacteria in an uncentrifuged urinary specimen.
Sulfa drugs, nitrofurantoin, cephalosporins, or quinolones may be used for the outpatient treatment of UTIs while the results of cultures are pending. Patients sick enough to be hospitalized may also be treated with intravenous aminoglycosides, medicine to treat nausea and vomiting, and hydration. The duration of therapy and the precise antibiotics used depend on the responsible organism and the underlying condition of the patient. Patients with anatomical abnormalities of the urinary tract, e.g., children with ureteropelvic obstruction or older men with bladder outlet obstruction, may sometimes require urological surgery.
The following conditions predispose sexually active women to development of UTI: the use of a contraceptive diaphragm, the method of sexual intercourse (greatly prolonged or cunnilingus), and failure to void immediately following intercourse.
Fluid intake should be increased to and maintained at six to eight glasses daily. Although cranberry and other fruit juices are often recommended for patients with UTI, there is little objective evidence to show they have an impact. The urinary tract anesthetic phenazopyridine and sitz baths may provide relief from perineal discomfort. The anal area should be wiped from front to back or wipe the front first to prevent carrying bacteria to the urethral area; the bladder should be emptied shortly before and after intercourse; the genital area should be washed before intercourse; if vaginal dryness is a problem, water-soluble vaginal lubricants should be used before intercourse; a contraceptive diaphragm, cap, shield, or sponge should not remain in the vagina longer than necessary. An alternative method of contraception should be considered.
Instructing the patient should emphasize self-care and prevention of recurrences. The antibiotic regimen should be explained, and the patient should be aware of signs and symptoms and , when they occur, should report them promptly to the primary caregiver.