Panton-Valentine Leukocidin (PVL) Positive Staph. Aureus

Panton-Valentine Leukocidin (PVL) is a toxin that is produced by some strains of Staphylococcus aureus and it increases its virulence. It is not a variation of MRSA and it can be produced by both methicillin resistant S. aureus (MRSA) and methicillin sensitive S. aureus (MSSA). Most of the PVL positive strains of S. aureus identified in the UK are sensitive to many antibiotics.

The staphylococcal toxin was described by Panton and Valentine in 1932.¹ PVL positive S. aureus were noted in the 1950s and 1960s in hospitals. Sporadic cases since have tended to be in the community rather than hospitals. PVL-producing MRSA can cause more serious infection but there is no evidence to suggest it is more dangerous than other types of MRSA. The PVL gene may not be the main virulence factor even in PVL strains.²

PVL positive MRSA has not been shown to spread more rapidly than any of the usual MRSA organisms.

• PVL producing MRSA is currently uncommon in hospitals in the UK.
• Less than 2% of Staph aureus are PVL positive³ and this includes both MRSA and MSSA. They occur in isolated outbreaks throughout the country. PVL positive strains are usually community acquired and generally affect previously healthy young children and young adults. This is in contrast with the hospital-associated MRSA strains which do not usually produce PVL and are more commonly associated with wound infections and septicaemia in elderly or severely ill patients in hospital.
• The Health Protection Agency (HPA) is aware of 7 deaths related to the organism in 2005 and 2006. Most were unrelated to hospital care.

• PVL strains of S. aureus most often present with cellulitis and purulent skin infections such as abscesses, boils and carbuncles.⁴
• Rarely they may produce more severe invasive infections, such as septic arthritis, bacteraemia or necrotising pneumonia (a severe, life-threatening form of pneumonia). ⁵
• There may be asymptomatic carriage.

Clinical infection tends to accompany other risk factors such as overcrowding, skin abrasions from contact sports, or using contaminated articles such as sharing towels, razors, poor hand hygiene and damaged skin from other conditions such as eczema.

Necrotising Pneumonia

This very serious infection can occur in previously healthy and immunologically competent young people. There is a high mortality rate.⁵

• There is usually no history of skin infection but often there is a preceding "flu-like" illness.
• Early clinical diagnosis is difficult but essential for survival.
• In general practice the following features are suggestive in a previously fit young person:
  • Haemoptysis
  • Hypotension
  • Severe sepsis following a "flu-like" illness.
• Admission to hospital is required.
• In hospital, these findings strongly suggest the diagnosis:
  • Multilobar infiltrates on chest X-ray, usually accompanied by effusions, and later cavitation.
  • Haemoptysis.
  • Hypotension.
  • Marked leucopenia.
  • Very high C-reactive protein level (>250-300 g/L) are not found in viral infections.
  • Gram film of sputum reveals sheets of staphylococcal-like Gram-positive cocci.
  • Non-specific findings of flu-like illness include fever of >39°, tachycardia >140 beats per minute, myalgia and chills.
  • Diarrhoea and vomiting may be due to associated toxic shock, which along with a significantly raised serum creatine kinase suggests myositis.

The CURB score of confusion, urea, respiratory rate, blood pressure, and age can be used to stratify patients with community acquired pneumonia into different management groups.⁶ In this condition, it may be misleadingly low in young adults on admission.

Swabs should be taken as indicated and if there is specific reason to suspect PVLSA, such as recent contact, it should be stated on the request form. A PCR test for PVL virulence genes and simultaneous discrimination of MRSA from MSSA has recently been developed.⁷

• Early treatment is preferable.
• Effective treatment is readily available. Usually the penicillinase resistant penicillins such as flucloxacillin will suffice but when there is resistance, the organism is usually sensitive to erythromycin, tetracycline, ciprofloxacin, rifampicin, trimethoprim and fusidic acid.
• Hospital treatment of necrotising pneumonia, usually involves a number of antibiotics given intravenously.

Recent evidence suggests that production of the toxins by this bacterium can be reduced by using antibiotics that inhibit cell wall synthesis and so they should be preferred. Beta lactams may produce a worse outcome in PVL-MRSA.⁸

Necrotising pneumonia has a high mortality rate if not diagnosed early and treated energetically. Otherwise, prognosis with this infection is generally good.

The risk of acquiring PVLSA is small but the HPA advises the public of a number of measures to prevent spread of the infection:

• Maintain routine hygiene measures, including proper cleansing and disinfection of cuts and minor wounds. Wounds should be dressed and covered until healed.
• Avoid contact with contaminated bandages and lesions.
• If spread or recurrence occurs, seek medical advice.
• Personal hygiene includes regular bathing or showering, regular changing of linen and underwear, hand washing, avoiding sharing personal items such as toothbrushes, face cloths or towels.
• Wash hands regularly.
• In shared facilities such as gyms, it is good practice to use liquid soap and disposable towels, to place a towel on the bench before sitting, and to ensure the facilities are cleaned frequently and that there is good ventilation to the locker room and showers.
• As with any kind of S. aureus, thorough hand washing and drying, or use of alcoholic hand rubs if hands are not visibly soiled, have been shown to be the most important measures in reducing cross-infection in both the community and the hospital.⁹
• If the infection is present in hospital, barrier nursing may be required.