BOSTON -- Wound botulism tied to subcutaneous injection of "black tar" heroin -- first reported 20 years ago -- appears to be problem that won't go away, with another case series described here.

Fifteen cases of the condition, all of which were serious enough to require mechanical ventilation, were seen from 2005 to 2015 at the Texas Tech University Health Sciences Center in El Paso in Texas, according to Ihtesham Qureshi, MBBS, and colleagues.

Action Points Note that this case series was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

The report also included a tip for other clinicians who might encounter the condition, which could occur anywhere that so-called "skin popping" is a popular way to inject heroin.

Qureshi's group, reporting in a poster presented at the American Academy of Neurology (AAN) annual meeting, found that nearly half of their patients had shown a normal pupillary light reflex -- thus indicating that this response "should not be used as a finding to exclude botulism."

They also noted that early recognition of the syndrome is key to starting effective treatment. All 15 patients survived and 13 were discharged to home.

The study was reported at AAN because botulism presents as a neuromuscular disorder, with visual abnormalities, limb weakness, and difficulty swallowing as common symptoms.

Although most cases of botulism occur from eating contaminated food, about 25%-30% begin as subdermal infections when Clostridium botulinum spores are introduced under the skin. Formerly it was seen mainly in victims of traumatic crush injury, but in the past few decades it has become increasingly associated with injection drug use, either from contamination of needles or of the injected substance.

Wound botulism has been a particular problem with black tar heroin, which is so named because it comes in sticky, dark chunks -- according to Qureshi's group, that is because the pure heroin is mixed with ground paper bits soaked in black shoe polish and dirt. For that reason, it can be problematic to inject intravenously, leading to alternate methods of administration including "skin popping," a slang term for shallow intradermal or intramuscular injection.

The first cases of wound botulism associated with injection drug use was reported in 1982. In the mid-1990s, several reports appeared tying wound botulism to injection of black tar heroin. More recently, in 2011, public health investigators in California published a 17-patient case series that specifically implicated skin popping.

All of the 15 cases seen in the El Paso center involved respiratory failure. Other common symptoms included those listed above, but each of those were lacking in some patients. Beyond the neuromuscular symptoms, though, they all showed skin abscesses that tipped the treating clinicians to a possible injection-drug complication.

Qureshi's group noted that black tar heroin use is especially common in southern border areas (the substance being imported mostly from Mexico), thus raising suspicion for wound botulism in cases of skin abscess combined with serious neuromuscular complaints.