Flesh-eating disease – or necrotizing fasciitis as its known medically – is fast, nasty and often fatal. The fact that you can get it from contact with seawater makes it even more scary! Should we not swim in the sea anymore? Avoid all seafood? Stay away from beaches, boats and wet markets? These are the sort of questions raised recently. This thread from concerned residents on the Discovery Bay Forum is a good example.
But hold on a minute! The case discussed in the forum actually turned out to have nothing at all do with beaches, seawater, shellfish fish or anything else marine. A common Streptococcus bacteria which lives all around us on our bodies and in our guts was the cause of that infection.
So don’t panic! It’s a fascinating topic, and I want to look at the facts and the data first and then bring things into perspective with a look at the history of marine flesh-eating disease in Hong kong. What exactly is the danger? How worried should we be?
What is flesh-eating disease?
It is a serious bacterial infection of the soft tissue. The bacteria don’t actually eat flesh but the toxins they release while multiplying kill off living cells around them. This can cause death within 12 and 24 hours and about 20 to 30 percent of cases are fatal.
Several different bacteria can cause it. The most common cause is group A Streptococcus, which lives in people’s throats or on their skin. The man in Discovery Bay who recently died actually contracted a type of Streptococcus. But other bacteria can also cause it, including some which naturally live in your guts, on your skin, in marine sediment and seawater, soil, decaying plants and other places. One type called methicillin-restistant Staphylococcus aureus – best known from the news as MRSA – has also become important in the last 10 years because it is resistant to almost all antibiotics and is a major problem in hospitals. And it doesn’t have to be one type of bacteria that causes flesh-eating disease, they can also act together in what is known as Type II or polymicrobial necrotizing fasciitis.
So you can’t avoid these bacteria as they are everywhere in the environment. However, to cause an infection with flesh-eating disease they need a way into your body, because skin will not let them in, but an open wound will give them a chance to grow. Even once inside, your immune system is a great defence, as long as the bacteria do not enter your bloodstream directly. The majority of reported cases are in people who for several possible reasons have a weakened immune system: e.g. underlying illness, chronic diseases, tumours, diabetes, alcoholism or immuno-surpressing drugs and these cases are most likely to be fatal if the infection enters the blood stream. In fact one of the test of Vibrio vulnificus involves injecting the bacteria into the blood stream of mice to see if they die….sometimes science is a bit grim…but still, it saves lives.
Most but not all of the cases reported in Hong Kong recently were all caused by a marine bacteria Vibrio vulnificus, a relative of the bacteria that causes cholera (Vibrio cholerae).
What is the danger from Vibrio vulnificus?
The bacterium is everywhere, both geographically and in a variety of environments, although it occurs in relatively low numbers. It is naturally present in warm seawater and is not linked to pollution, although some studies have found higher numbers of this bacteria in tar balls (e.g. washed up tar balls from the Deep-water Horizon Oil spill), which attract many kinds of bacteria. It likes brackish (mixed fresh and seawater) and so is more common in estuaries and near river mouths. Because it likes warm water, it is more common in the summer months. Infection occurs through open wounds or through eating raw or undercooked shellfish or fish, but is not transmissible between persons. Anyone can be affected by wound infections, but persons with underlying medical conditions, especially liver disease, are at increased risk of blood stream infection and serious complications.
Vibrio vulnificus infections happen worldwide: the US, Japan, Southern Europe etc. In Taiwan, an annual number of 13-26 cases were reported during 1996-2000. The incubation period is usually 12 to 72 hours and the symptoms are intense pain, redness, swelling and rapidly developing tissue destruction usually associated with some form of wound. In persons with underlying medical conditions, especially liver disease, it can cause bloodstream infections with fever, chills, decreased blood pressure, blistering skin lesions and even death in severe cases. In healthy persons, it can cause diarrhoea, vomiting and abdominal pain. Sometimes, the swelling starts at the site of minor injury such as a small cut or bruise, but in other cases there is no obvious source of infection. Bloodstream infections in persons with liver disease are fatal about 50% of the time.
The infection is treated with antibiotics to kill the bacteria as soon as possible, but patients may also need surgery to cut away infected dead tissue or amputate the affected limb. Other than that, those who recover suffer no long-term consequences.
What is the dangerous it in Hong Kong?
In the last 7 years (since May 2005), there have been 51 reported cases of Vibrio vulnificus infections in Hong Kong – 37 Men and 14 women – an average of about 7 cases a year. To put this into perspective, in 2011 there were 6 reported cases of leprosy and in 2010 there were 124 reported snake bites in Hong Kong.
Infections occur predominantly in the summer months from May to October when the water is warm and conditions are right. Isolated cases also appear in colder months, but this could simply be because fish or shellfish is often kept in warmer tanks or because fresh seafood is now globally traded and flown around the world and imported from warmer regions.
Although the fatality rate is high at 27%, with 32% for men and 14% for women. The average age of infected persons was 66 for men and 71 for women.
From about July 2011 the Department of Health also reported if cases had underlying illnesses, and this shows that at least 53% of cases had underlying illness (3% did not have underlying illness and for the remaining cases the Centre for Health Protection’s press releases did not have enough information). I have compiled the data as a spreadsheet which you can download for free by clicking this link.
So basically, if you are older and/or weakened by illness or chronic disease you are at risk if you suffer a wound from handling seafood or have an open wound that comes into contact with uncooked seafood or seawater. Otherwise, there is no need to worry yourself greatly.
You should of course follow the CHP’s advice on prevention, which is more or less common-sensical:
* Avoid foot/leg contact with dirty water when visiting wet market;
* Avoid exposure of open wounds or broken skin to seawater or salty water;
* Wounds should be thoroughly cleaned and properly covered; and
* Wear thick rubber gloves when handling raw shellfish.
* You should seek medical advice promptly if you develop symptoms and signs of infection such as increasing redness, pain and swelling.
As V. vulnificus is so fond of warm brackish water, consider this: climate change is a leading cause of warming seas around the world, as well as of increased freshwater run-off from more erratic and heavier rain storms caused by the higher evaporation of seawater. This means that one of the effects of climate change could be an increase in infections, because the ideal conditions for V. vulnificus are becoming more widespread. There is a very direct and personal reason to cut your carbon foot-print, especially if you like shellfish and beach holidays…