Pseudomonas Infections

Definition

A pseudomonas infection is caused by a bacterium, Pseudomonas aeruginosa, and may affect any part of the body. In most cases, however, pseudomonas infections strike only persons who are very ill, usually hospitalized.

Description

P. aeruginosa is a rod-shaped organism that can be found in soil, water, plants, and animals. Because it rarely causes disease in healthy persons, but infects those who are already sick or who have weakened immune systems, it is called an opportunistic pathogen. Opportunistic pathogens are organisms that do not ordinarily cause disease, but multiply freely in persons whose immune systems are weakened by illness or medication. Such persons are said to be immunocompromised. Patients with AIDS have an increased risk of developing serious pseudomonas infections. Hospitalized patients are another highrisk group, because P. aeruginosa is often found in hospitals. Infections that can be acquired in the hospital are sometimes called nosocomial diseases.

Of the two million nosocomial infections each year, 10% are caused by P. aeruginosa. The bacterium is the second most common cause of nosocomial pneumonia and the most common cause of intensive care unit (ICU) pneumonia. Pseudomonas infections can be spread within hospitals by health care workers, medical equipment, sinks, disinfectant solutions, and food. These infections are a very serious problem in hospitals for two reasons. First, patients who are critically ill can die from a pseudomonas infection. Second, many Pseudomonas bacteria are resistant to certain antibiotics, which makes them difficult to treat.

P. aeruginosa is able to infect many different parts of the body. Several factors make it a strong opponent. These factors include:

• the ability to stick to cells
• minimal food requirements
• resistance to many antibiotics
• production of proteins that damage tissue
• a protective outer coat

Infections that can occur in specific body sites include:

• Heart and blood. P. aeruginosa is the fourth most common cause of bacterial infections of the blood (bacteremia ). Bacteremia is common in patients with blood cancer and patients who have pseudomonas infections elsewhere in the body. P. aeruginosa infects the heart valves of intravenous drug abusers and persons with artificial heart valves.
• Bones and joints. Pseudomonas infections in these parts of the body can result from injury, the spread of infection from other body tissues, or bacteremia. Persons at risk for pseudomonas infections of the bones and joints include diabetics, intravenous drug abusers, and bone surgery patients.
• Central nervous system. P. aeruginosa can cause inflammation of the tissues covering the brain and spinal cord (meningitis ) and brain abscesses. These infections may result from brain injury or surgery, the spread of infection from other parts of the body, or bacteremia.
• Eye and ear. P. aeruginosa can cause infections in the external ear canal—so-called "swimmer's ear"—that usually disappear without treatment. The bacterium can cause a more serious ear infection in elderly patients, possibly leading to hearing problems, facial paralysis, or even death. Pseudomonas infections of the eye usually follow an injury. They can cause ulcers of the cornea that may cause rapid tissue destruction and eventual blindness. The risk factors for pseudomonas eye infections include: wearing soft extended-wear contact lenses; using topical corticosteroid eye medications; being in a coma; having extensive burns; undergoing treatment in an ICU; and having a tracheostomy or endotracheal tube.
• Urinary tract. Urinary tract infections can be caused by catheterization, medical instruments, and surgery.
• Lung. Risk factors for P. aeruginosa pneumonia include: cystic fibrosis; chronic lung disease; immunocompromised condition; being on antibiotic therapy or a respirator; and congestive heart failure. Patients with cystic fibrosis often develop pseudomonas infections as children and suffer recurrent attacks of pneumonia.
• Skin and soft tissue. Even healthy persons can develop a pseudomonas skin rash following exposure to the bacterium in contaminated hot tubs, water parks, whirlpools, or spas. This skin disorder is called pseudomonas or "hot tub" folliculitis, and is often confused with chickenpox. Severe skin infection may occur in patients with P. aeruginosa bacteremia. The bacterium is the second most common cause of burn wound infections in hospitalized patients.

Causes and symptoms

P. aeruginosa can be sudden and severe, or slow in onset and cause little pain. Risk factors for acquiring a pseudomonas infection include: having a serious illness; being hospitalized; undergoing an invasive procedure such as surgery; having a weakened immune system; and being treated with antibiotics that kill many different kinds of bacteria (broad-spectrum antibiotics).

Each of the infections listed above has its own set of symptoms. Pseudomonas bacteremia resembles other bacteremias, producing fever, tiredness, muscle pains, joint pains, and chills. Bone infections are marked by swelling, redness, and pain at the infected site and possibly fever. Pseudomonas meningitis causes fever, headache, irritability, and clouded consciousness. Ear infection is associated with pain, ear drainage, facial paralysis, and reduced hearing. Pseudomonas infections of the eye cause ulcers that may spread to cover the entire eye, pain, reduced vision, swelling of the eyelids, and pus accumulation within the eye.

P. aeruginosa pneumonia is marked by chills, fever, productive cough, difficult breathing, and blue-tinted skin. Patients with cystic fibrosis with pseudomonas lung infections experience coughing, decreased appetite, weight loss, tiredness, wheezing, rapid breathing, fever, blue-tinted skin, and abdominal enlargement. Skin infections can cause a range of symptoms from a mild rash to large bleeding ulcers. Symptoms of pseudomonas folliculitis include a red itchy rash, headache, dizziness, earache, sore eyes, nose, and throat, breast tenderness, and stomach pain. Pseudomonas wound infections may secrete a blue-green colored fluid and have a fruity smell. Burn wound infections usually occur one to two weeks after the burn and cause discoloration of the burn scab, destruction of the tissue below the scab, early scab loss, bleeding, swelling, and a blue-green drainage.

Diagnosis

Diagnosis and treatment of pseudomonas infections can be performed by specialists in infectious disease. Because P. aeruginosa is commonly found in hospitals, many patients carry the bacterium without having a full-blown infection. Consequently, the mere presence of P. aeruginosa in patients does not constitute a diagnostic finding. Cultures, however, can be easily done for test purposes. The organism grows readily in laboratory media; results are usually available in two to three days. Depending on the location of the infection, body fluids that can be tested for P. aeruginosa include blood, urine, cerebrospinal fluid, sputum, pus, and drainage from an infected ear or eye. X rays and other imaging techniques can be used to assess infections in deep organ tissues.

Treatment

Medications

Because P. aeruginosa is commonly resistant to antibiotics, infections are usually treated with two antibiotics at once. Pseudomonas infections may be treated with combinations of ceftazidime (Ceftaz, Fortraz, Tazicef), ciprofloxacin (Cipro), imipenem (Primaxin), gentamicin (Garamycin), tobramycin (Nebcin), ticarcillin-clavulanate (Timentin), or piper-acillin-tazobactam (Zosyn). Most antibiotics are administered intravenously or orally for two to six weeks. Treatment of an eye infection requires local application of antibiotic drops.

Surgery

Surgical treatment of pseudomonas infections is sometimes necessary to remove infected and damaged tissue. Surgery may be required for brain abscesses, eye infections, bone and joint infections, ear infections, heart infections, and wound infections. Infected wounds and burns may cause permanent damage requiring arm or leg amputation.

Prognosis

Most pseudomonas infections can be successfully treated with antibiotics and surgery. In immunocompromised persons, however, P. aeruginosa infections have a high mortality rate, particularly following bacteremia or infections of the lower lung. Mortality rates range from 15 to 20% of patients with severe ear infections to 89% of patients with infections of the left side of the heart.

Prevention

Most hospitals have programs for the prevention of nosocomial infections. Patients with cystic fibrosis may be given periodic doses of antibiotics to prevent episodes of pseudomonas pneumonia.

Minor skin infections can be prevented by avoiding hot tubs with cloudy water; avoiding public swimming pools at the end of the day; removing wet swimsuits as soon as possible; bathing after sharing a hot tub or using a public pool; cleaning hot tub filters every six weeks; and using appropriate amounts of chlorine in the water.

Resources

OTHER

Centers for Disease Control. 〈http://www.cdc.gov/nccdphp/ddt/ddthome.htm〉.

KEY TERMS

Bacteremia— Bacterial infection of the blood.

"Hot tub" folliculitis— A skin infection caused by P. aeruginosa that often follows bathing in a hot tub or public swimming pool.

Immunocompromised— Having a weak immune system due to disease or the use of certain medications.

Nosocomial infection— An infection that is acquired in the hospital.

Opportunistic— Causing disease only under certain conditions, as when a person is already sick or has a weak immune system.

Pathogen— Any microorganism that produces disease.

Melioidosis

Definition

Melioidosis is an infectious disease of humans and animals caused by a gram-negative bacillus found in soil and water. It has both acute and chronic forms.

Description

Melioidosis, which is sometimes called Pseudomonas pseudomallei infection, is endemic (occurring naturally and consistently) in Southeast Asia, Australia, and parts of Africa. It was rare in the United States prior to recent immigration from Southeast Asia. Melioidosis is presently a public health concern because it is most common in AIDS patients and intravenous drug users.

Causes and symptoms

Melioidosis is caused by Pseudomonas pseudomallei, a bacillus that can cause disease in sheep, goats, pigs, horses, and other animals, as well as in humans. The organism enters the body through skin abrasions, burns, or wounds infected by contaminated soil; inhalation of dust; or by eating food contaminated with P. pseudomallei. Person-to-person transmission is unusual. Drug addicts acquire the disease from shared needles. The incubation period is two to three days.

Chronic melioidosis is characterized by osteomyelitis (inflammation of the bone) and pus-filled abscesses in the skin, lungs, or other organs. Acute melioidosis takes one of three forms: a localized skin infection that may spread to nearby lymph nodes; an infection of the lungs associated with high fever (102°F/38.9°C), headache, chest pain, and coughing; and septicemia (blood poisoning ) characterized by disorientation, difficulty breathing, severe headache, and an eruption of pimples on the head or trunk. The third form is most common among drug addicts and may be rapidly fatal.

Diagnosis

Melioidosis is usually suspected based on the patient's history, especially travel, occupational exposure to infected animals, or a history of intravenous drug. Diagnosis must then be confirmed through laboratory tests. P. pseudomallei can be cultured from samples of the patient's sputum, blood, or tissue fluid from abscesses. Blood tests, including complement fixation (CF) tests and hemagglutination tests, also help to confirm the diagnosis. In acute infections, chest x rays and liver function tests are usually abnormal.

Treatment

Patients with mild or moderate infections are given a course of trimethoprim-sulfamethoxazole (TMP/SMX) and ceftazidime by mouth. Patients with acute melioidosis are given a lengthy course of ceftazidime followed by TMP/SMX. In patients with acute septicemia, a combination of antibiotics is administered intravenously, usually tetracycline, chloramphenicol, and TMP/SMX.

Prognosis

The mortality rate in acute cases of pulmonary melioidosis is about 10%; the mortality rate for the septicemic form is significantly higher (slightly above 50%). The prognosis for recovery from mild infections is excellent.

Prevention

There is no form of immunization for melioidosis. Prevention requires prompt cleansing of scrapes, burns, or other open wounds in areas where the disease is common and avoidance of needle sharing among drug addicts.

Resources

BOOKS

Pollock, Matthew. "Infections Due to Pseudomonas Species and Related Organisms." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.

KEY TERMS

Osteomyelitis— An inflammation of bone or bone marrow, often caused by bacterial infections. Chronic melioidosis may cause osteomyelitis.

Septicemia— Bacterial infection of the bloodstream. One form of melioidosis is an acute septicemic infection.

melioidosis (mee-li-oi-doh-sis) n. a disease of wild rodents caused by the bacterium Pseudomonas pseudomallei. It can be transmitted to humans, causing pneumonia, multiple abscesses, and septicaemia.