Despite two recent hospital outbreaks of bacteria that produce the Panton-Valentine leucocidin (PVL) toxin, Britain is not facing an epidemic of dangerous strains of Staphylococcus aureus, says the Health Protection Agency's expert on methicillin resistant S aureus (MRSA).
Angela Kearns said that although incidence “waxes and wanes” over time, recent cases in England implicate at least three different strains. “While we are seeing an overarching PVL related pattern of disease here, we're definitely not seeing an epidemic of a single strain.”
The latest outbreak, reported three days before Christmas, involved a neonatal unit at Norfolk and Norwich University Hospital. Six premature babies were affected by methicillin sensitive, PVL positive S aureus. One developed an active infection and has died; the hospital's chief executive, Paul Forden, said that the bacterium “may have played a part in the death.”
The other five babies did not develop active infection and are now in isolation, undergoing treatment with antibiotics. A consultant microbiologist, Judith Richards, said they were doing well.
Until now only one death is believed to have been caused by an infection transmitted in hospital. That case involved a patient who died in March at the University Hospital of North Staffordshire in Stoke-on-Trent, from PVL positive MRSA. A nurse who died in September at the same hospital, Maribel Espada, is now known to have contracted the infection elsewhere, said Dr Kearns. She said, “Fourteen cases have been identified by the hospital this year, including two retrospectively identified just before Christmas.”
A previous outbreak of PVL positive S aureus affected 10 mothers and babies in the maternity unit of Derriford Hospital, Plymouth, in 2003. Those cases involved methicillin sensitive bacteria, though not the same strain as in the Norwich outbreak. At least 14 strains of PVL positive S aureus are known.
Less than 2% of S aureus bacteria produce the PVL toxin, which was first identified in the United Kingdom in the 1930s. Subsequent “look-back” research indicated that such bacteria date back to at least the beginning of the 20th century and are not a result of antibiotics used in humans. In the 1990s methicillin resistant strains began to emerge.
“It's only recently that we've had tests with good sensitivity and specificity,” said Dr Kearns, adding that some previous outbreaks may have gone unnoticed. Because of a lack of mandatory surveillance programmes, the lethality of the disease remains unknown, but the Health Protection Agency is now studying the issue, she said.
PVL positive S aureus was most common in the 1950s and 1960s, affecting people in Britain, Australia, and the United States. Most outbreaks are sporadic and confined to individuals. Seven people have died of community acquired PVL positive S aureus in Britain in the past three years.
Dr Kearns recommended that anyone finding a new boil or abscess should “see their GP or accident and emergency department, depending on the time of day.” She added, “Hospital staff or GPs should take samples for microbiological analysis so we can get better capture of how many cases are out there. Microbiological labs should send the isolates to us at the reference laboratory.”
Skin to skin transmission is possible, she said. “We've certainly seen cases cropping up in the young and healthy, maybe because they've been in close contact with one another, playing contact sports, for example. So we're seeing a new pattern of disease.”