Microbiologist Amy Horneman (Baltimore Sun )
The story of a 24-year-old Georgia graduate student fighting a flesh-eating disease has prompted a microbiologist with the Veterans Affairs Maryland Health Care System to speak out about the infection.
Aimee Copeland lost most of her left leg after the flesh-eating bacteria necrotizing faciitis is believed to have entered a cut on her leg, according to the Associated Press, which reports she may also have to have her fingers amputated. The waterborne bacteria Aeromonas hydrophila is believed to have caused the infection.
Microbiologist Amy J. Horneman, director of microbiology/molecular diagnostics at the Maryland VA who holds a doctorate in marine and estuarine environmental sciences, said the bacteria is more common than believed. She is not involved in Copeland's case but talks about the infection.
What is Aeromonas?
The microorganism Aeromonas is a member of a family of 29 species of bacteria that are ubiquitous or indigenous to a variety of aquatic environments worldwide. These include freshwater sources such as lakes, ponds, rivers and streams, as well as brackish water like the Chesapeake Bay and drinking and surface waters, especially recreational.
Of the 29 published species of Aeromonas, only eight are routinely isolated from cases of human disease, such as diarrhea, wound infections, respiratory, ocular, and bloodstream infections. Some other serious infections caused by this organism include necrotizing fasciitis [flesh-eating] and hemolytic uremic syndrome, or kidney failure. One of the major species within this group of eight is known as Aeromonas hydrophila, which actually means "water-loving."
How common is it for people to become infected with this particular bacterium?
It is hard to determine since many cases — such as diarrhea — may go unreported. Since this group of organisms, including A. hydrophila, are naturally occurring inhabitants of water sources worldwide, we as humans become infected when we come in contact with this organism and either ingest it through a recreational water source or have an open cut or a wound that is exposed to the aeromonads in the water.
The numbers of aeromonad organisms increase in the warmer months from April to October, and therefore, when we engage in water-related activities in these warmer spring and summer months, such as fishing, boating, swimming and skiing, we are recreationally exposing ourselves to these aquatic bacteria in their natural environment. We also get infected with this organism by ingesting contaminated water or undercooked seafood and/or food that has been stored at refrigeration temperatures for a long time, as this organism can grow at low temperatures.
Although immuno-compromised people are more prone to be infected, immuno-competent individuals of all age groups are susceptible to infection. Specifically, diarrhea is more common in the very young (less than 5 years of age) and elderly. Importantly, the isolation rate of this organism from children suffering from diarrhea is about the same in developed versus underdeveloped countries. Although in most cases, proper hydration leads to recovery of infected people, once the organism finds its way in the bloodstream, aggressive antibiotic treatment is needed.
Who can get the infection?
In past years, it was thought to be an opportunistic pathogen only seen in immuno-compromised humans, but there are increasing numbers worldwide and numerous published case reports of both intestinal and extraintestinal (wounds, septicemia) human diseases documenting that it is a serious pathogen in humans of all ages.
What are the symptoms?
The symptoms related to Aeromonas infections are no different than those of other types of diarrheal or wound infections. However, when it is a serious and deep aquatic wound infection, clinicians should immediately think of Aeromonas as the possible culprit, especially if the patient is exhibiting signs of "necrotizing fasciitis." The syndrome of necrotizing fasciitis or infection with "flesh-eating" bacteria can be associated with a number of different bacteria, including Streptococcus Group A, Staphylococcus aureus, and Vibrio vulnificus [marine bacterium found in salt water ocean sources and the brackish Chesapeake Bay]. However, if it's a fresh or brackish water-related wound, physicians should be considering Aeromonas first as the cause of this rapidly, fulminating serious infection.
I've always called this organism "the Rodney Dangerfield" of pathogens because it is underappreciated and doesn't get the respect it deserves as a human pathogen.
How do you treat it?
The majority of the Aeromonas isolates causing human diseases are unfortunately nearly universally resistant to penicillin, ampicillin, amoxicillin and 1st generation cephalosporins, but can generally be successfully treated with ciprofloxacin, Septra (SXT, Bactrim), and second- and third-generation cephalosporins.
How common or uncommon is it for people to die from the diseases caused by Aeromonas?
It is difficult to know the exact incidence of Aeromonas infections worldwide because Aeromonas is not a reportable condition in the United States or in most other worldwide countries. In my 30 years of research on this enigmatic bacterium, I have collected more than 500 clinical samples from various Maryland residents from one end of the Chesapeake Bay to the other and the surrounding river tributaries from a number of clinical sources, including diarrhea, sepsis and serious wound infections. Additionally, I have collected several hundred more isolates from any number of human cases from around the world for my continuing current research studies here at the Baltimore VA Medical Center. Likewise, other investigators working with aeromonads across the world have collected hundreds of isolates for their respective studies.