An infection is the presence and growth (colonization) of a microorganism within a living host, usually resulting in harm to the host. Such infective microorganisms are called pathogens. Pathogens can be bacterial, viral, or fungal in nature. The sole purpose of pathogens is to reproduce within the cells or tissue of the host, compromising body functions and damaging tissue. Viruses reproduce by inserting their own genetic material (DNA or RNA) into the host cell, and then using the host's biochemical machinery to replicate. The extent of infection varies depending on the number of microorganisms, their ability to cause illness (virulence), and the body's ability to defend against them (immune response). Tissue damage can occur directly or from substances produced by the pathogen (e.g., toxins, enzymes). Localized infections affect one particular tissue or area of the body, whereas systemic infections affect the whole body. Bacterial infections can be local (e.g., cellulitis, abscess) or systemic (bacteremia, sepsis). Fungal infections typically are local. Viral infections generally are systemic (e.g., mumps, measles, HIV) with some exceptions (e.g., herpes, conjunctivitis).
Infections are acquired in many different ways. Pathogens can be consumed (e.g., Clostridium botulinum, salmonella) or inhaled (influenza virus, Mycobacterium tuberculosis). Some pathogens acquire access to the body through a break in the skin or mucous membranes (e.g., Neisseria gonorrhoeae, HIV). Organisms not usually harmful (normal flora) may move from a part of the body where they normally exist to another part of the body where they can cause damage. For example, the bacterium E. coli is a normal inhabitant of the intestinal tract, but it causes serious illness if ingested or relocated to the urinary tract. Bacteria that normally colonize the upper respiratory tract, groin, or skin of otherwise healthy individuals (e.g., Staphylococcus aureus) may become opportunistic and invade body tissue, especially if an open wound is present due to injury or surgery. This can result in local and systemic infection and can occur quite rapidly. Bacterial infections can be hospital acquired (e.g., through urinary catheters, intravenous lines or catheters) or community acquired (e.g., from individuals in regular contact within a closed environment such as a school or prison).
Infections can spread from individual to individual in a variety of ways. Airborne pathogens are discharged into the air from the respiratory tract of an infected individual through coughing or sneezing. They may be inhaled by another individual, settle on clothing, walls, floors, and other surfaces where they are picked up by another individual, or be transmitted by direct contact (e.g., kissing, bodily contact, sharing utensils). Other pathogens can live on or in the body of individuals who do not experience symptoms but transmit the pathogens to others (carriers). Prenatal infection occurs when the mother passes an infection to her infant during pregnancy, either through the placenta or from fetal contact with maternal membranes during birth. Infections also can spread through insect vectors such as mosquitoes or ticks (e.g., malaria, Lyme disease), through animal carriers (e.g., rabies), in contaminated food, when soil enters the body through wounds (e.g., tetanus), or through ingesting contaminated water (e.g., typhoid, dysentery, cholera).
Risk: Injury, surgery, chronic illness, and a weakened immune system (immune system compromise or immunosuppression) can increase risk for infection. The very young and the elderly are at increased risk compared to the rest of the population because their immune systems are weakened and less able to respond effectively.
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Source: Medical Disability Advisor
History: Symptoms of an infection vary greatly depending on the primary site of infection. Inflammation is the common symptom; it may be indicated by fever if systemic or organ system infection is present or redness of the skin, increased heat, swelling, pain and loss of function if local infection is present. Other symptoms vary considerably. For example, meningitis is associated with headache, stiffness and pain in the neck, and difficulty turning and bending the head (nuchal rigidity), whereas appendicitis is associated with pain in the lower abdomen, nausea, and vomiting. Fever may be present in both types of infection. Symptoms of an upper respiratory infection may include headache, cough, and nasal discharge; tissue of the nose and throat may appear red and inflamed and infective (purulent) material may be present or produced with coughing. Symptoms of a gastrointestinal infection may include nausea, vomiting, and diarrhea. The common cold is a viral infection of upper respiratory tract with symptoms that may include runny nose, nasal obstruction, sneezing, sore throat, cough, and hoarseness, as well as general symptoms such as chills, fever, headache, aching muscles (myalgias), and a vague feeling of discomfort or illness (malaise).
Physical exam: Physical examination findings depend on where the infection is located and whether it is local or systemic. When examined by touch (palpated), the area around a local infection may feel warm and touching the area may elicit pain. Discharge from an abscess may be present. A systemic infection may not cause any specific localized abnormalities, but pain, fever, and sometimes confusion may be noted, depending on the original site of infection and the specific pathogen. Diagnosis may rely on history, symptoms, and testing. Vital signs, including pulse, blood pressure, respiration, and temperature, may be affected.
Tests: A complete blood count (CBC) with differential to evaluate white blood cell (WBC) count and immune system response may indicate the presence of an infection irrespective of its site. Erythrocyte sedimentation rate (ESR) and C-reactive protein may be measured to determine inflammation levels. Urinalysis may reveal bacteria or excess white cells indicative of urinary tract infection. Examining the stool for white blood cells may indicate an infectious process that involves the gastrointestinal tract.
A microbial culture of an infected site often identifies the bacterial organism responsible for the infection, and sensitivity testing may indicate an appropriate antibiotic for treatment. Fluid or purulent material from an infected site may be obtained for culture and sensitivity before antibiotics are started to optimize the opportunity for a positive culture. This may involve removal (aspiration) of the fluid with a needle and syringe. Culture and sensitivity testing requires 24 to 48 hours to grow the causative bacteria, which may delay treatment; the physician may opt to start empirical antibiotic therapy after the sampling based on the presumptive diagnosis, with modification of the treatment, if necessary, when the results of the cultures and sensitivity testing are available. Based on the location of an infection, tests to assess the extent of the infection include chest x-ray, abdominal ultrasound, sinus films, computed tomography (CT), magnetic resonance imaging (MRI), or spinal tap.
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Source: Medical Disability Advisor
Rest and adequate fluid intake are important factors in the recovery from any infection. Individuals with pain or muscle aches may need pain-relieving medicine (analgesics). Those with fever may require fever-reducing medicine (antipyretics). Other treatments vary depending on the responsible pathogen, the tissues or organ systems involved, and the health status of the individual.
Bacterial infections are treated with antibiotics. The specific antibiotic used is either chosen based on experience (empirically) or based on the sensitivity as indicated by culture and sensitivity testing. If the infection has become walled off (abscess), it usually is opened (incised) and allowed to drain. Severe systemic bacterial infections (e.g., meningitis, bacteremia, septicemia) may require hospitalization and intravenous (IV) antibiotic administration.
A viral infection may or may not be treated with an antiviral medication. It is difficult to design drugs that kill the virus inside cells without also killing the host cells that they live in. Therefore, treatment of viral infections depends largely on relieving the symptoms while relying on the body's immune system to eradicate the virus. If the individual has a compromised immune system, antiviral drug therapy may be necessary. Generally antiviral drug therapy must be started with 24 to 48 hours of acquiring the infection to be maximally effective.
Fungal infections (mycoses) are treated with antifungal drugs based on the location of the infection. Skin and nail fungal infections (e.g., athlete's foot) generally are treated with antifungal creams or lotions applied to the skin. Antifungal drugs also are available in tablet, lozenge, suspension, vaginal suppositories, and injection forms for more serious or less accessible fungal infections. Fungal infections in immunocompromised individuals such as those with HIV infection can be quite serious and may require antifungal drugs administered intravenously (IV).
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Source: Medical Disability Advisor
Bacterial infections usually can be cured by early and appropriate antibiotic therapy, but if the immune system is overwhelmed and organ systems fail, infection can be fatal. Complications such as organ system failure increase the risk of disability and death. The very young and the elderly are at increased risk of complications. If the individual is immunocompromised by either HIV infection/AIDS, immunosuppressive therapy for cancer treatment or for prevention of transplant rejection, recovery is slower, with an increased risk of death due to the underlying disease and the individual's inability to respond to the infection.
In healthy individuals, fungal infections generally can be cured through administration of antifungal drugs; in immunocompromised individuals, fungal infections may be chronic and life threatening. Some infections are incurable and may become chronic and controlled to a variable degree (e.g., genital herpes). |
Source: Medical Disability Advisor
Infection can cause death to body tissue (necrosis), requiring removal of tissue (débridement) or amputation of the affected body part (e.g., gangrene). Infections can progress to life-threatening diseases, including, but not limited to, pneumonia, meningitis, encephalitis, botulism, tetanus, typhoid, and cholera. An infection also can spread beyond the local area of involvement and into the bloodstream, causing potentially fatal sepsis or bacteremia.
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Source: Medical Disability Advisor
Accommodations may include time off from work to allow the individual to rest and prevent transmission of infection to coworkers and to the public. Restrictions will vary depending on the nature of the infection and the job requirements of the individual. For example, a chef with an upper respiratory or gastrointestinal (GI) infection should not prepare food; a nurse with influenza should avoid patient contact; a construction worker with a hand infection may be temporarily limited in the type of work he or she can do.
In some cases, complications can result in permanent disability (e.g., gangrene resulting in amputation). Some infections are incurable and become chronic (e.g., HIV, herpes).
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Source: Medical Disability Advisor
| If an individual fails to recover within the expected maximum duration period, the reader may wish to consider the following questions to better understand the specifics of an individual's medical case. Regarding diagnosis:
- Did individual present with symptoms of local infection or systemic infection? Was fever present? Was the skin or tissue of the upper respiratory system inflamed?
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Was the pathogen identified?
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Was method of transmission identified? Was an insect vector or animal carrier involved? Was food or water supply contaminated?
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Has individual recently had an injury or surgery?
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Is individual immunocompromised?
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Has the site of infection been identified?
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On exam, was the affected area tender to palpation? Was the area warm?
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Was the exam normal with no specific findings?
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Has a CBC with differential, ESR, C-reactive protein been done?
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Have culture and sensitivity testing done?
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Depending on the location of the infection, has a chest x-ray been done? Ultrasound? Other x-rays? CT or MRI? Spinal tap?
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Have conditions with similar symptoms been ruled out?
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Regarding treatment:
- Has individual received rest, fluids, analgesics, and antipyretics, as needed?
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Is infection bacterial? Has individual been treated with the appropriate antibiotic?
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Is infection viral? Has individual received appropriate treatment? Are antiviral medications required?
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Is infection fungal? Has individual been treated with the appropriate antifungal medication?
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Were comorbidities appropriately managed?
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Were preventive techniques instituted to diminish likelihood of spread of the infection?
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Regarding prognosis:
- Can individual's employer accommodate any necessary restrictions?
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Does individual have any conditions that may affect ability to recover?
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Have any complications occurred that may affect recovery?
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Source: Medical Disability Advisor
| CitedPorter, Robert S., et al., eds. "Biology of Infectious Disease." The Merck Manual of Diagnosis and Therapy. 18th ed. Whitehouse Station, NJ: Merck and Company, Inc., 2008. Merck Manuals Online. Jul. 2009. Merck & Co., Inc. 26 Oct. 2009 <http://www.merck.com/mmpe/sec14/ch167/ch167a.html>. |
Source: Medical Disability Advisor
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