ORLANDO, Fla. - Summer is just around the corner, and aquatic organisms should be considered in the differential diagnosis for a wound infection if the patient was exposed to aquatic or coastal areas, according to William A. Burke, MD.
While Staphylococcus and Streptococcus are still the most common bacteria isolated from water-related infections, several varieties of marine organisms are isolated from infections each summer, said Burke, professor and head of the dermatology section, East Carolina University School of Medicine, Greenville, N.C.
The big four marine infections include:
E. rhusiopathiae, a gram-negative pleomorphic rod, is often confused with Listeria in the laboratory, Burke said. E. rhusiopathiae loses its cell wall and forms L-forms in tissue, which makes if difficult to culture. Recreational and occupational history is important in diagnosis.
"It's very easy to culture from the bloodstream, but not from the skin," he said.
This bacterium causes erysipeloid, which is similar to erysipelas, but is not as severe; usually the patient is afebrile and does not suffer from regional adenopathy or malaise. However, both conditions are treated with pen i cillin or amp icil lin, a first-generation ceph alosporin or erythromycin. E. rhusiopathiae is resistant to vancomycin. Children and adults can be treated with the same medications, Burke said.
The most common reaction of erysipeloid is a self-limited, localized infection, most commonly on the hand. The reaction develops into a bright red, well-demarcated plaque which can burn or itch.
Patients with disseminated infection are usually febrile, blood cultures are positive for E. rhusiopathiae and endocarditis is relatively common. The localized erysipeloid lesion is still sometimes present with disseminated infection.
In rare cases, septic arthritis, intracranial abscess and pulmonary involvement may occur.
E. rhusiopathiae is widely distributed in nature and is found in fresh and salt water. Infections from the bacterium are often found in fishermen, fish handlers, seafood processors, farmers and poultry workers.
M. marinum is an acid-fast, photochromogen rod in the atypical or environmental mycobacteria. Incubation time is seven to 14 days and the bacterium does not grow well at 37° F.
"Incubation time can be as long at 21 days, and laboratories should be informed to culture the organism at 32° F," he said.
Anyone who is frequently around water is at risk for this infection. This includes anyone who owns a fresh-water aquarium. The infection is often seen in fishermen, boaters and aquatic sports enthusiasts.
"We don't see it as commonly in children as we do in adults, but the kids are swimming in the river and have other activities that expose them to it," Burke said.
The initial lesion begins within several weeks after exposure to the organism and presents as a small papule at the inoculation site, which appears most commonly over a bony prominence. The lesion enlarges over a four- to eight-week period into a verrucous nodule. The infection may spread via lymphatics in a sporotrichoid manner, which Burke said is commonly seen in his practice. Bones and joints can be affected in rare occasions and the infection rarely disseminates.
A biopsy is needed to diagnose M. marinum.
The recommended treatment for children is trimethoprim-sulfamethoxazole (TMP-SMX). Adults can be treated with minocycline (100 mg twice daily), TMP-SMX, rifampin (Rifidan, Hoechst Marion Roussel) with ethamubutol (Myambutol, Lederle Labs), or clarithromycin (Biaxin, Abbott). However, surgical excision will sometimes rid the infection. Burke also recommends using heat as an adjunctive therapy.
"I use heat as an adjunctive therapy. It [heat] not only kills the organism but it also increases the amount of antibiotic that goes to the area, by increasing blood flow," he said.
A. hydrophila, a gram-negative facultatively anaerobic rod, is ubiquitous in nature, can be found in fresh and salt water, usually brackish, and is a common fish pathogen.
"It's found everywhere. It's not related to pollution, etc. It's just there," Burke said.
The organism can be acquired via the gastrointestinal (GI) tract leading to gastroenteritis or may cause wound infections with cellulitis, fasciitis, myonecrosis, gas/gangrene and eventual sepsis in immunocompromised or liver disease patients.
Infection with A. hydrophila can also result in pneumonia, meningitis, endocarditis, osteomyelitis, septic arthritis and an ecthyma gangrenosum-like syndrome in patients with sepsis. Wound infections are often mixed with Staphylococcus and immunocompromised patients and those with liver disease are at highest risk for disseminated disease.
With the more serious infections like Aeromonas and Vibrio risk factors play a part in developing serious infections, but most children don't have serious disease, Burke said. Kids with lymphoproliferative disorders, those on immunosuppressive medication or those with immunodeficiencies are at a higher risk for serious infection.
Recommended treatment for A. hydrophila is incision, drainage, exploration and cleansing of the wound site. Children should be treated with TMP-SMX, and adults can be treated with oral antibiotics, fluoroquinolones/norfloxacin, TMP-SMX, tetracycline/doxycycline or chloramphenicol. Parenteral drugs, including fluoroquinolones, imipenem with cilastatin (Primaxin, Merck), or a third-generation ceph alosporin, are also options.
V. vulnificus is a serious Vibrio infection, and patients often present in septic shock, Burke said. V. vulnificus is a gram-negative, curved facultatively anaerobic rod with a single polar flagellum and can be found in salt water and brackish water.
V. vulnificus manifests in two forms: primary septicemia and secondary septicemia. In primary septicemia, which is usually derived from eating raw or undercooked seafood (most commonly oysters), the infection is presumably acquired via the GI tract, although usually with no GI symptoms, Burke said.
Secondary septicemia can occur following a penetrating injury and starts with a cellulitis developing within one to two days after inoculation.
Burke stressed that V. vulnificus is an extremely virulent organism with rapid progression to necrotizing fasciitis, myonecrosis, gangrene and sepsis.
Patients with liver disease, diabetes, those who are immunocompromised or anyone taking immunosuppressive medication are at risk for this infection.
"People with these risk factors should be advised not to eat raw or undercooked shell fish," said Burke, who also mentioned that the Centers for Disease Control and Prevention provides recommended seafood cooking times and instructions for proper cooking on its web site.
Septic patients may have petechiae, purpura, necrotic pustules, bullae or conditions that mimic ecthyma gangrenosum. Mortality from septicemia with this organism is 40% to 60%.
With wound infections, treatment should involve incising, draining and cleansing the wound. Adults with early, uncomplicated wound infections with no risk factors should be treated with tetracycline or doxycycline. Doxycycline plus ceftazidime or chloramphenicol should be administered parenterally if the condition becomes more complicated; ceftazidime alone should be used for children. Infection due to other Vibrio organisms usually responds well to fluoroquinolones and TMP-SMX.
For more information:
- Burke WA. Cutaneous infections of the coast. Presented at the 56th American Academy of Dermatology Annual Meeting. Feb. 27-March 4. Orlando, Fla.
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