A case of Panton – Valentine leucocidin toxin-positive Staphylococcus aureus-mediated neonatal mastitis

Received 31 July 2014 Accepted 1 September 2014 Department of Clinical Microbiology, University Hospital Limerick, Limerick, Ireland Centre for Interventions in Infection, Inflammation & Immunity (4i), Graduate-Entry Medical School, University of Limerick, Limerick, Ireland Department of Surgery, University Hospital Limerick, Limerick, Ireland Department of Paediatrics, University Hospital Limerick, Limerick, Ireland


Introduction
Staphylococcus aureus is a commensal skin organism, a major human and veterinary pathogen, and the most common cause of human mastitis (Osterman & Rahm, 2000;Peton & Le Loir, 2014;Rasigade & Vandenesch, 2014;Uhlemann et al., 2014).As such, considerable emphasis has been placed on elucidating the mechanisms by which the virulence of S. aureus strains is mediated (Rasmussen et al., 2013;Sollid et al., 2014).Amongst these mechanisms are the horizontal transfer of the chromosomal cassette conferring resistance to methicillin (SCCmec) (Nubel et al., 2008) and ability to produce toxins such as (but not limited to) Panton-Valentine leucocidin (PVL) mediating tissue necrosis (Labandeira-Rey et al., 2007;Diep et al., 2010).
In the context of maternal and infant health, many studies have described incidence and transmission of communityassociated and healthcare-associated strains, in addition to recommended antibiotic regimens, invasive and noninvasive management, and prevention strategies including decolonization (Saiman et al., 2003;Fortunov et al., 2007;Alsubaie et al., 2012;Jahanfar et al., 2013;Sheffield, 2013).With respect to mastitis specifically, most reports relate to incidence and treatment of S. aureus maternal infection (Branch-Elliman et al., 2012;Chick et al., 2012;Iatrakis et al., 2013;Perez et al., 2013) and, to a lesser degree, subsequent transmission of infection to (mostly pre-term and neonatal) infants (Behari et al., 2004;Gastelum et al., 2005;Kayiran et al., 2014).Mastitis in children is less common and is largely related to neonates and pubescent/ postpubescent age groups (Faden, 2005).A case series of neonates demonstrated that mastitis occurred most commonly in the fourth and fifth weeks of life, although Abbreviation: PVL, Panton-Valentine leucocidin.
age ranged from 12 to 45 days, and that parenteral antibiotics eradicated causative microorganisms (Stricker et al., 2005).A larger review of neonatal cases from 2005 to 2011 (in Atlanta, USA) concluded that S. aureus was the most common cause of mastitis and that no infant with a positive breast culture had a concordant positive culture elsewhere (Montague et al., 2013), arguing that urine, blood and spinal fluid cultures are unnecessary in otherwise well, afebrile infants with mastitis.
PVL-positive clones are emerging as virulent, multidrugresistant S. aureus in Ireland (prevalence of PVL-positive MRSA increased from 0.2 to 8.8 %, and that of PVLpositive MSSA decreased from 20 to 2.5 % between 2002 and 2011) (Shore et al., 2014).Despite this, we believe this report to be the first description of neonatal mastitis caused by PVL-bearing S. aureus and its successful treatment and, as such, will make a contribution to the emerging debate regarding management of neonatal mastitis (Al Ruwaili & Scolnik, 2012).

Case report
A 20-day-old female infant was admitted to University Hospital Limerick (UHL) on 16 December 2013.She was born at 41 weeks gestation via spontaneous vaginal delivery.At day 7 of life, her mother noted that the baby's right breast was swollen and red.When it failed to settle spontaneously, she brought the baby to her general practitioner who diagnosed right breast mastitis and commenced what proved to be ineffective antimicrobial therapy with oral amoxicillin.The right breast continued to increase in size and the infant's condition deteriorated, with poor feeding, irritability, lethargy and vomiting.The infant's parents self-referred to the hospital.On arrival at UHL, examinations revealed discrete areas of erythema suggestive of mastitis on both breasts, more marked on the right.Under the right nipple there was a 4 cm swelling with underlying yellow-green discoloration of the skin.The area was warm and tender to touch, with pain elicited on superficial palpation.There was no obvious pointing over the right abscess.A 1.5 cm swelling was identified under the left nipple with no associated topical changes.The infant was diagnosed with bilateral mastitis, complicated on the right side with early abscess formation.She was apyrexial.
Haematological investigations demonstrated a normal white cell count (16.24610 9 l 21 ), elevated neutrophils (8.48610 9 l 21 ), mild thrombocytosis (427610 9 l 21 ) and normal haemoglobin count (14.4610 9 l 21 ).Renal function was normal.C-reactive protein was raised at 11 mg l 21 .Blood cultures were not completed, while urine was free of pathogens.A superficial swab of the right breast abscess resulted in growth of coagulase-negative staphylococci, but too few to enumerate accurately.Initially, the neonate was treated conservatively with intravenous flucloxacillin (220 mg four times per day) and intravenous benzylpenicillin (220 mg three times per day), but exhibited minimal improvement.At 3 days, a small area of necrotic skin developed on the right breast in the periareolar area.Intravenous benzylpenicillin was discontinued, intravenous flucloxacillin was continued and oral clindamycin (25 mg four times per day) was introduced, as (due to increasing prevalence as described above) there was clinical suspicion of PVL toxin-mediated staphylococcal infection.Subsequently, at 5 days, 5 ml aspirate was surgically removed from the infant's right breast abscess, which proved positive for S. aureus resistant to amoxicillin and gentamicin and sensitive to flucloxacillin, levofloxacin, linezolid, rifampicin, vancomyin and tetracycline.Intraoperative examination under anaesthesia confirmed a contralateral left breast abscess from which 2 ml S. aureuspositive aspirate was removed.
Post-operative antimicrobial therapy involved oral clindamycin and intravenous flucloxacillin.Both isolates of S. aureus subsequently tested positive for PVL toxin.Antimicrobial therapy was modified to oral clindamycin for a further 7 days, at which point full resolution had been achieved.Subsequently, staphylococcal protein A (Spa) typing identified the isolate as being t005 (EMRSA-15) (http:// spa.ridom.de/spa-t005.shtml),which has been reported mostly in Europe (including the UK and Ireland), ranked ninth in 2010 with respect to relative incidence (Grundmann et al., 2010).

Discussion
Reports of neonatal mastitis are relatively uncommon (Stauffer & Kamat, 2003) but most frequently (ca.85 %) caused by S. aureus (Holmes & Zadoks, 2011).As such, there is some debate regarding best practice in its management (Al Ruwaili & Scolnik, 2012), but recommended treatment involves antibiotic therapy followed by surgical incision and drainage or needle aspiration if medical management fails (Sloan & Evans, 2003).
In this case, we describe the first incidence of PVL-positive S. aureus-caused neonatal breast abscess.It seems reasonable that risk factors for neonatal acquisition of PVLpositive S. aureus would be similar to those for other S. aureus strains, i.e. ingestion of infected breast milk, impaired skin integrity, or infection of breast tissue (engorged due to maternal hormones) via the nipple (Stauffer & Kamat, 2003).The long-term consequences of neonatal mastitis and its treatment were reported by Panteli et al. (2012), whereby development of the breast was characterized as involving intraductal dilatation, fibrous elements and calcifications or, where surgical incision was required, breast asymmetry and significant reduction in size compared with the uninfected breast.The emergence of PVL toxin-positive S. aureus (Labandeira-Rey et al., 2007;Rasmussen et al., 2013;Shore et al., 2014) is adding a new perspective to neonatal mastitis incidence due to its ability for tissue necrosis and the potential damage that this may cause to infected infants (Hsieh et al., 1999;Nazir, 2005).
In this case, specifically, the neonate was breastfed successfully for 4 days postpartum and subsequently switched to bottle-feeding for convenience.The baby's mother did not have any underlying recurrent infective skin or soft tissue infections.This family had not been washing domestic items such as towels used for this neonate separately to those in use for other members of the family.During the course of the neonatal infection no other family member presented with signs or symptoms of a PVLassociated infection.Vaginal carriage of S. aureus is possible; however, samples obtained from high vaginal and groin areas proved negative.The potential for zoonosis (Holmes & Zadoks, 2011) was eliminated as the family did not have a household pet and did not live on a farm, and there was no other direct contact with animals.As this was an isolated incident, environmental (i.e.delivery room and equipment) and staff screening was considered unnecessary.
The vigilance of the infant's parents and the relatively early identification of PVL-positive S. aureus meant that appropriate targeted (rather than empiric) antimicrobial therapy resulted in eradication of the pathogen.The revision of therapy was influenced to no small part by the availability of aspirated pus, rather than topical swabs, which underwent on-site molecular and conventional susceptibility testing, as described elsewhere (O'Connor et al., 2014), which reduced time to diagnosis by at least 24 h through avoidance of culture on non-selective solid media.It is debatable whether non-invasive assessment such as sonography would have been useful in this case, although its use has been described in differentiating between neonatal abscesses and mastitis (Borders et al., 2009).

Conclusion
Neonatal PVL toxin-positive S. aureus mastitis and breast abscess formation is uncommon but suspicion should arise with poor response to conventional antimicrobial therapy for mastitis.There is a need to improve awareness of PVLpositive S. aureus, particularly among those caring for neonates, as early diagnosis can prevent complications of invasive tissue necrosis and potential for long-term consequences such as abnormal breast development.Sending appropriate samples for testing can expedite diagnosis.