During February 2004–September 2006, several family clusters of skin and soft tissue infections were observed in a suburban area south of Milan in northern Italy. The patients lived in or near the town of Codogno and sought treatment at the outpatient clinic of the local hospital. In each of the family clusters, the first identified case was a newborn child or a mother who had recently delivered in the Codogno Hospital. In 2006, another cluster of skin and soft tissue infections was observed in young patients who lived in different households in the same suburban area.

Medical records and microbiologic data regarding skin and soft tissue infections occurring in neonates or mothers examined in the Codogno Hospital from 2003 through 2005 were reviewed. At the time of the review, the hospital was a 220-bed facility, serving a community of ≈15,000 inhabitants. The maternity ward comprised 7 rooms with a total of 13 beds and was part of the Department of Obstetrics and Gynecology. The department had 45 staff members that included obstetricians, midwives, nurses, and support staff. Annually, ≈600 deliveries were performed. The newborn nursery was under the direction of the Department of Pediatrics and included 2 rooms, 1 room for changing and feeding the babies and the other room with 14 cribs for the neonates. The nursery staff included 9 neonatal nurses and 1 general nurse, but 16 additional staff members were shared across the Department of Pediatrics. The median length of stay of neonates in the nursery was 4 days. A follow-up visit was performed at a dedicated hospital clinic 10–15 days after discharge.

Bacteriologic specimens were obtained for culture from the largest infected body area with a sterile swab or needle and were processed in the microbiology laboratory of the Codogno Hospital according to standard methods. Swabs obtained from anterior nares were plated directly onto salt mannitol agar plates and blood agar plates without a preenrichment step. Plates were incubated for 24 h in ambient air and 5% CO₂, respectively. Identification of isolates and antimicrobial susceptibility tests were performed with an automatic system (Vitek 2; bioMérieux, Marcy l’Etoile, France). The susceptibility pattern was confirmed by the disk-diffusion method following Clinical and Laboratory Standards Institute guidelines (16).

Further molecular tests and genotyping were performed on all S. aureus isolates that had been stored. Bacterial DNA was prepared with a commercial kit (QIAamp DNA Mini Kit; QIAGEN GmbH, Hilden, Germany). Species identification and methicillin susceptibility were confirmed by a duplex PCR assay with primers targeting nuc and mecA genes, respectively. Detection of the presence of the genes lukS-PV and lukF-PV coding for the 2 subunits of the PVL toxin was obtained by PCR (17).

To analyze clonal relatedness of the strains, all available isolates were submitted to pulsed-field gel electrophoresis (PFGE) and to a sequence-based method that detects variations in the short sequence repeat (SSR) region of the protein A gene (spa typing) (18). For PFGE, total genomic DNA embedded in agarose plugs was digested with SmaI and separated by using a previously described method (19). Profiles of strains that differed by fewer than 3 bands were considered to belong to the same PFGE type (20). For spa typing, PCR amplification of the SSR region was performed according to the protocol of Shopsin et al. (18). Sequences were obtained and analyzed by using an Internet-based software Ridom Staph Type (www.ridom.de/spaserver). Selected isolates underwent multilocus sequence typing (MLST) according to the recommended method (21). The allelic profiles obtained were compared with those deposited in the MLST database (http://saureus.mlst.net).

To ascertain the spread of S. aureus in the maternity ward and nursery of the hospital, we performed screening for S. aureus nasal colonization on neonates, mothers, and medical and nonmedical staff who worked in the Departments of Pediatrics and Obstetrics and Gynecology. Two separate surveys were performed, the first in July 2005 and the second in December 2005, after implementation of enhanced infection control measures.

Five familial clusters of skin and soft tissue infections, involving 2–5 family members, were observed in the Codogno area. The first case in each cluster occurred in 2004 or early 2005, but infections in other household members or recurrent infections continued to be observed until 2006. In all families, the onset of infection was associated with a neonate born in the Codogno Hospital or a mother who had recently delivered in the same hospital.

Furunculosis and abscesses were the most common clinical features and relapses were common (Table 1). Furunculosis of the prepuce developed in a neonate in family 1 four days after birth in the Codogno Hospital in February 2004. His father sought treatment for recurrent subcutaneous axillary abscesses later in 2004 and in 2005, and a leg abscess developed in his mother in September 2006.

The mother in family 2 sought treatment for an infection in the vulva, groin, and inner thighs in August 2004, ten days after delivering at the Codogno Hospital. Several recurrences of abscesses in the same areas occurred as well as in this patient’s left buttock and leg until 2006. In 2005, furunculosis developed in the father on his nose and scalp, and recurring pustules developed on the inner thighs of 2 siblings over 2 months.

In family 3, a subcutaneous facial abscess developed in the mother in January 2005, two months after she delivered at the Codogno Hospital; subsequently, a vulvar abscess and recurrent abscesses of the right leg continued to develop in this patient until 2006. The child had a leg abscess in June 2006.

Family cluster 4 involved 5 persons: a neonate, a sibling, both parents, and the maternal grandmother. Pustules developed on the neck and groin of the neonate 4 days after birth at the Codogno Hospital in January 2005 and subsequently, subcutaneous abscesses developed in the axilla and forearm. Over the same time multiple subcutaneous abscesses developed in the axillae and on the forearms and legs of both parents and the elder sibling. The grandmother had a facial abscess in July 2005, and the father contracted furunculosis of the left forearm in September 2006.

Family cluster 5 involved both parents of a child who was born in the Codogno Hospital in December 2004 but who did not experience skin infections. Facial pustules developed in the mother in February 2005, two months postpartum. Subsequently, she was treated for a leg abscess and axillary furunculosis. In March 2006, a subcutaneous abscess developed in the thigh of her husband in March 2006.

All cases with a bacteriologic diagnosis were caused by MSSA that showed a distinct susceptibility pattern: resistant to penicillin and gentamicin and susceptible to oxacillin, erythromycin, tetracycline, rifampicin, and ciprofloxacin. Nasal swabs were performed in 7 patients from the clusters and were positive for MSSA in 6.

During March–June 2006, eleven additional cases of S. aureus skin and soft tissue infections occurred in patients who lived in the same area in different households and who were not related to the family clusters. With the exception of a case caused by CA-MRSA/ST8 in an infant 3 years of age (22), the other 10 cases were caused by MSSA. Nine patients were children ranging in age from 6 months to 11 years. Two infants (Table 1, patients 20 and 23) had experienced a pustular rash 1 year earlier, soon after birth in the Codogno Hospital. Clinical signs included pustulosis or furunculosis (3 patients) and abscesses (7 patients). One patient also had conjunctivitis. Patients were neither immunosuppressed nor had preexisting skin infections or other risk factors.

Antimicrobial drugs, mostly oral amoxicillin-clavulanic acid, were given to patients based on their clinical conditions and site and size of the infected area (23) (Table 1). A recurrence of a large subcutaneous abscess in 1 adult patient led to treatment with intravenous teicoplanin. Spontaneous drainage occurred in 4 abscesses, and surgical incision and drainage were performed in 3 cases. All patients had a favorable outcome.

Isolates available for molecular typing included 5 MSSA from family clusters 2, 3, and 4, and 10 MSSA from the sporadic cases in 2006. All isolates from the family clusters and 7 of the 10 isolates from the sporadic cases contained PVL genes. By PFGE, all PVL-positive isolates appeared indistinguishable or closely related (differing by 1–2 bands) and were assigned to PFGE type A. These isolates also exhibited an identical spa type, corresponding to t005. MLST of 6 representative isolates yielded sequence type (ST) 22 (Table 1). Isolates with these characteristics will be subsequently referred to as the “epidemic MSSA clone.” Three PVL-negative MSSA isolates, obtained from infections in 2006, showed different PFGE, spa, and MLST types (Table 1).

Examination of medical records and microbiologic data from the Codogno Hospital showed a cluster of postpartum mastitis involving 13 women that had occurred from October 2003 through January 2004, before the family clusters were identified. The women had delivered in the same hospital 2–12 weeks before the onset of symptoms. In 6 case-patients, mastitis had progressed to breast abscesses and required surgical drainage. Culture of the drainage yielded MRSA in 1 case-patient and MSSA in the other case-patients. MSSA isolates had a susceptibility pattern identical to that of the community-acquired MSSA. Molecular studies were not performed on these isolates.

In early 2004, several cases of skin infections (mainly pustulosis of the groin or upper thigh) were observed in neonates in the hospital nursery or after discharge when they were examined during routine follow-up visits. From January through March 2004, 14 such skin infections were observed. No other cases were identified until December 2004, when 9 cases occurred. From January through September 2005, skin infections developed in a total of 65 neonates, with peak incidence in June and July when 14 and 17 cases were identified, respectively. In July 2005, screening for nasal S. aureus carriage was initiated, and infection control measures were enforced (see Infection Control Measures). Cases of infection gradually diminished, and no new cases were observed after September 2005. MSSA isolates were obtained from all neonates whose specimens had been cultured with skin infections in 2004 and 2005, but the isolates were not stored and were not available for molecular studies.

To ascertain the circulation of S. aureus in the Codogno Hospital, screening for S. aureus nasal carriage was performed in the maternity ward and the nursery in July 2005 and in December 2005, after implementation of infection control measures. In July 2005, nasal swabs were obtained from 48 neonates, 58 mothers, and 71 medical and nonmedical personnel. MSSA was isolated from 19 (39.6%) of 48 neonates in the nursery, 16 (27.6%) of 58 mothers, and 19 (26.8%) of 71 staff (Table 2). No MRSA strain was identified. Remarkably, all of the 17 available isolates from neonates were PVL-positive and 16 corresponded to the epidemic MSSA clone. Only 1 maternal and 3 staff isolates corresponded to the epidemic MSSA clone. Personnel colonized with the epidemic MSSA included 1 pediatrician, 1 newborn nurse, and 1 nurse in the Department of Obstetrics and Gynecology. One of the neonates was colonized by a PVL-positive MSSA that had a PFGE profile, spa type, and MLST that were completely different from those of the epidemic MSSA. MSSA isolates that were PVL-negative were genotypically heterogeneous, showing a number of different PFGE profiles and spa types (data not shown).

In the December 2005, screening, nasal swabs were obtained from 43 neonates, 17 mothers, and 64 staff. No neonate was colonized with S. aureus, although 5 (29.4%) of 17 mothers and 4 (6.2%) of 64 staff members carried MSSA. In addition, a staff member was colonized with MRSA. Only 1 isolate from a mother corresponded to the epidemic PVL-positive MSSA clone, which suggests that although transmission inside the nursery had been interrupted, the epidemic strain was still circulating in the community. Two pediatric nurses were colonized by PVL-positive MSSA isolates that showed PFGE types, spa types, and STs that were unrelated to the outbreak MSSA clone (Table 2).

In all cases but 1, results of spa typing were in accordance with the PFGE analysis, by clustering the isolates belonging to the epidemic clone and discriminating genetically different isolates. The exception was a PVL-positive MSSA isolate obtained from a neonatal nurse in the July screening. This isolate was PFGE type A that had a novel spa type (t2336) resulting from deletion of 4 of the 12 repeats of t005, and yielded a novel combination of MLST alleles (ST954) that was a single locus variant of ST 22.

When the neonatal outbreak of skin infections was identified in December 2004, contact precautions were instituted in the nursery and the maternity ward for staff and mothers, who were required to wear a gown and mask when feeding their babies. In June 2005, these control measures were expanded to include enhanced contact precautions based on existing recommendations to control the spread of MRSA and other drug-resistant microorganisms (24). Notices to promote handwashing among personnel as well as among mothers and visitors were posted on the walls of the nursery and waiting areas. The nursery and adjacent areas were deeply cleaned with chlorine-containing disinfectant. After nasal carriage screening in July 2005, intranasal mupirocin was administered to all neonates and was continued until hospital discharge, usually for 5 days. Personnel and mothers with MSSA-positive nasal cultures received nasal mupirocin for 5 days with or without a 3-day course of amoxicillin/clavulanate. After the introduction of these measures, cases of MSSA skin infections in neonates decreased and no new cases occurred in the hospital after September 2005, no infections were reported at follow-up visits, and no neonates in the nursery carried S. aureus in the December 2005 nasal screening.