The HSE has warned gardaí about a batch of contaminated heroin that has led to six addicts being hospitalised over two days in Dublin.

The HSE has identified six suspected cases of wound botulism, which if not treated can lead to abscesses in the muscles, contamination of the blood, organ failure and eventual death.

Botulism is a rare condition caused by a poison which is produced by a bacterium, clostridium, which is common in the soil but can be deadly when mixed with heroin.

The six heroin users who were hospitalised last week developed wound botulism after 'skin popping' the class A drug. This occurs when users inject heroin just below the skin's surface rather than directly into a vein, giving users a less intense experience that lasts longer. At least two of the victims are believed to be in a serious condition.

Wound botulism is caused by a toxin that is commonly found as spores in soil. The illness can be caused if a wound is contaminated by soil or gravel. But in recent years this type of botulism has been most commonly reported among chronic drug users. It occurs mainly in skin abscesses from injecting heroin but can also be caused by snorting cocaine.

Detectives around Dublin have been made aware of the situation as have drug treatment centres so that heroin users can be warned about the possibility of contracting the condition.

The last cases of botulism in drug users in Ireland occurred in 2002 when three injecting users developed it.

More than 90% of cases can be treated but some have proved fatal. Those who died in the last outbreak in the UK are thought to have not sought medical attention soon enough.

Drug users have been advised to use as little citric acid as possible and refrain from sharing needles, as the bacterium may be transmitted via citric acid.