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Methicillin-resistant Staphylococcus aureus infections among healthy full-term newborns
  1. L James1,2,
  2. R J Gorwitz2,
  3. R C Jones1,
  4. J T Watson1,
  5. J C Hageman2,
  6. D B Jernigan2,
  7. Y Lord3,
  8. N Caballes3,
  9. C Cortes1,
  10. R G Golash4,
  11. J S Price4,
  12. S I Gerber1
  1. 1
    Chicago Department of Public Health, Chicago, Illinois, USA
  2. 2
    Centers for Disease Control and Prevention, Atlanta, Georgia, USA
  3. 3
    St Anthony Hospital, Chicago, Illinois, USA
  4. 4
    Illinois Department of Public Health Division of Laboratories, Chicago, Illinois, USA
  1. Dr L James, Ministry of Health, College of Medicine Building, 16 College Road, Singapore 169854; lynjames36{at}yahoo.com

Abstract

Objective: Methicillin-resistant Staphylococcus aureus (MRSA) strains have emerged in the community, causing disease among healthy people lacking traditional risk factors for MRSA infection. This article describes an outbreak of MRSA among healthy full-term newborns.

Design: Cases were identified and corresponding medical information collected. Telephone interviews were conducted with mothers of cases ands surveillance cultures from mothers and newborns were performed. MRSA isolates were genotyped.

Setting: Hospital in Chicago, Illinois, USA.

Participants: Newborns, their mothers and hospital healthcare workers.

Intervention: Nursery infection control practices were enhanced. The MRSA-colonised healthcare workers received intranasal mupirocin.

Main outcome: Within 4–23 days of birth, 11 newborns were identified with pustules, vesicles or blisters located on the head, groin, perineum, ears, legs, chin and trunk. All received antimicrobials and recovered without incident.

Results: None of 432 peripartum women, one of 399 newborns, and two of 135 healthcare workers were nasal MRSA carriers. Available isolates from six patients, two healthcare workers, and one from an MRSA-colonised newborn were similar by pulsed-field gel electrophoresis. Other than contact with the hospital, no common exposures of MRSA transmission were identified.

Conclusions: MRSA strains that initially emerged in the community are now causing disease in healthcare settings. Providers should be aware that MRSA can cause skin infections among healthy newborns. Adherence to standard infection control practices is important to prevent transmission of MRSA in nurseries.

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Methicillin-resistant Staphylococcus aureus (MRSA) was first isolated in UK hospitals in 1961. Since then MRSA has been responsible for an increasing number of healthcare-associated infections.1 Established risk factors for healthcare-associated MRSA (HA-MRSA) infection include2:

  • history of hospitalisation, surgery, dialysis or residence in a long-term care facility within 1 year before the MRSA culture date;

  • presence of an indwelling catheter or percutaneous medical device at the time of culture;

  • previous isolation of MRSA.

Since the late 1990s, MRSA infections with onset in the community have been reported among seemingly healthy people, often children and young adults, who lack traditional risk factors for infection with MRSA.210 Unlike HA-MRSA infections, community-associated MRSA (CA-MRSA) infections present most commonly as skin and soft tissue infections, notably furuncles and abscesses, although invasive infections also occur.2

Genes for the cytotoxin, Panton–Valentine leukocidin (PVL), associated with primary S aureus skin infections and necrotising pneumonia, have been identified frequently in isolates from CA-MRSA infections, but rarely in isolates from HA-MRSA infections.6 11 12 Two pulsed-field gel electrophoresis (PFGE) types, termed USA300 and USA400 according to a typing scheme developed at the Centers for Disease Control and Prevention (CDC) in Atlanta, USA, have accounted for the majority of isolates from CA-MRSA infections characterised to date in the USA; these differ from the MRSA genotypes prevalent in most healthcare facilities.13 14

CA-MRSA has been reported in community settings where people are in close contact (eg, athletic teams, military training facilities, correctional facilities and childcare centres).1521 MRSA strains with microbiological characteristics typical of strains that emerged in the community have recently caused infections in neonatal intensive care units.22 23 One recent report described an outbreak of MRSA infections caused by pulsed-field type USA400 among healthy full-term newborns and postpartum mothers resident in or recently discharged from a hospital in New York.24 Healthcare workers but not the mothers were screened for MRSA colonisation, and none were identified as being colonised with the outbreak strain.

In this report, we describe the investigation of an outbreak of pulsed-field type USA300 MRSA skin infections among otherwise healthy full-term newborns born at a single hospital in Chicago, Illinois, USA, during which the potential roles in transmission of nasal and vaginal colonisation in the mother and nasal colonisation in healthcare workers were assessed.25

METHODS

In October 2004, the Chicago Department of Public Health was notified by the hospital’s infection-control practitioner of a cluster of seven MRSA skin infections among healthy full-term newborns delivered at the hospital. MRSA skin infections had not been identified among newborns managed at the hospital before this cluster. The 178-bed hospital has a nursery for relatively well newborns who might require observation or such special treatment as phototherapy for jaundice or encouragement to feed.

Case definition and identification of cases

A case was defined as an infection in a newborn aged <30 days, delivered at the hospital between 1 May 2004 and 21 January 2005, with one or more skin lesions from which MRSA was isolated. To detect additional cases among the hospital’s newborns who were hospitalised after discharge or brought to the hospital’s emergency department or paediatric and well-baby clinics, regular reminders were sent to all healthcare staff at the hospital to encourage reporting of potential cases immediately to the hospital’s infection control practitioner. In addition, the infection control practitioner reviewed all microbiology reports for MRSA-positive cultures among newborns.

Epidemiological investigation

Staff from the Chicago Department of Public Health reviewed the medical records of affected patients and their mothers for demographic and clinical information. A telephone interview was conducted with the mothers by using a standard questionnaire to obtain information on the patient’s current health, medical history and activities since discharge from the newborn nursery, including common neonatal practices (eg, circumcision and baptism). Mothers were also asked about their baby’s exposure to people with established HA-MRSA risk factors, employment in a healthcare field, history of skin infection, or links to settings where CA-MRSA outbreaks have occurred (eg, among competitive sports team members and correctional facilities).

We did surveillance cultures for MRSA colonisation on newborns and peripartum women between 8 November 2004 and 21 January 2005, and healthcare workers associated with the nursery, labour and delivery, and postnatal wards from 1 to 31 January 2005. Nares specimens were obtained from: all newborns at discharge; all peripartum women on admission to labour and delivery and discharge from the postnatal wards; and all healthcare workers in the nursery, labour and delivery, and postnatal wards. In addition, vaginal specimens for culture were collected from all peripartum women on admission to labour and delivery.

Laboratory investigation

MRSA isolates were genotyped by PFGE by using SmaI-digested DNA, and gels were analysed as previously described.13 19 All MRSA isolates were tested for the genes encoding PVL by multiplex real-time polymerase chain reaction (PCR) by using primers prepared at CDC.26

RESULTS

Patient characteristics

Eleven patients with MRSA skin infections were identified, all born at full-term with normal birth weights and Apgar scores. Six (55%) infections were clustered in the months of September and October 2004 (fig 1).

Figure 1 Epidemic curve of patients (n = 11) by onset of MRSA skin infection, May 2004 to January 2005.

The median age at the time of onset of infection was 7 days (range 4–23 days); nine (82%) patients were boys, and nine (82%) had been born by caesarean delivery. Median length of stay in the hospital after delivery was 4 days (range 3–10 days). One patient had symptoms of infection 6 days after birth while still in hospital. Symptoms started after discharge among the remaining 10 patients, with symptom onset occurring at a median of 5 days (range 1–18 days) after discharge from the nursery. All patients were of Hispanic origin, consistent with the racial demographics of the hospital’s catchment area. None underwent circumcision, while in the hospital or after discharge.

Clinical presentation

The patients presented with skin lesions that were described as pustules, vesicles or blisters. Table 1 presents the clinical information for the patients. Because of the limited size of the individual lesions, surgical drainage was not performed for any patient. One patient was hospitalised for 2 days for observation as a result of his infection. All patients recovered without incident. During their hospital stay after birth, two patients received diagnoses of neonatal jaundice, and one required phototherapy. Another patient was noted to have a ventricular septal defect confirmed on echocardiogram but was otherwise well. For the remaining eight patients, the hospital stay after birth was uneventful, and no procedures were performed, including insertion of intravenous lines, arterial catheterisations, intubations, phototherapy and radiographic studies.

Table 1 Clinical information for the babies infected with methicillin-resistant Staphylococcus aureus (MRSA)

Interviews with mothers

Mothers of nine (82%) of 11 patients were interviewed; two could not be reached because of incorrect contact information. Other than contact with the hospital, no common exposures or likely sources of MRSA transmission outside the hospital were identified by the mothers. The fathers of two of the patients participated in group sports, but neither was aware of skin disease or MRSA infections occurring among their associated sports participants.

Surveillance cultures

Of the 432 peripartum women from whom nasal and vaginal surveillance cultures were obtained, 30 (6.9%) and 10 (2.3%) were colonised with methicillin-susceptible S aureus (MSSA) in the nares and vagina, respectively. MRSA was not identified among any peripartum women. MSSA was isolated from the nares of 14 (3.5%) of 399 newborns at the time of discharge, and MRSA was isolated from the nares of 1 (0.3%) newborn.

Two (1.5%) of 135 healthcare workers, a doctor and a nursery nurse, were identified as being nasal MRSA carriers, and nine (6.7%) were colonised with MSSA. Both MRSA-colonised healthcare workers had had contact with newborns in the nursery. The doctor had attended one of the patients before infection occurred, and the nurse was on duty in the nursery during the birth stay of all the patients.

Laboratory results

The nine available isolates (six patient isolates, two healthcare worker isolates and one isolate from an MRSA-colonised newborn) were PFT USA300 and contained PVL genes. Isolates from the two healthcare workers and five patients were indistinguishable from one another by PFGE and also indistinguishable from MRSA strain USA300-0114, which has been associated with CA-MRSA outbreaks and sporadic infections in multiple states.19 Another strain of PFT USA300 was isolated from the remaining patient and the MRSA-colonised newborn.

Control measures

To prevent further transmission of MRSA in the nursery, adherence to standard infection control measures, namely hand hygiene and environmental cleaning in the nursery, were more strictly enforced through in-service training and direct observation. Although gowning and gloving were practised sporadically, universal gowning and gloving were not recommended. No changes were made to the bathing and rooming procedures for newborns.

In addition, the two MRSA-colonised healthcare workers were restricted from work as soon as culture results had been obtained. They were treated with intranasal mupirocin twice a day for 5 days to eliminate MRSA colonisation. No MRSA was identified on a second nasal culture, taken a day after mupirocin treatment was completed. The two healthcare workers returned to clinical work after the results of the second nasal cultures were obtained, and no additional follow-up was performed. No additional cases have been identified among newborns delivered at the hospital since December 2004.

DISCUSSION

What is already known on this topic

  • Strains of MRSA that cause skin and soft tissue infections in previously healthy people have been described since the late 1990s.

  • These strains have usually been typed by PFGE as USA300 or USA400.

  • They are different types of PFGE than the ones identified in the healthcare setting.

What this study adds

  • This investigation describes a strain of MRSA that has been associated with previously health people in the community.

  • This MRSA strain was identified in newborns born at a single hospital.

This report documents an outbreak of MRSA skin infections caused by PFT USA300 among healthy full-term newborns born at a single hospital. This outbreak description is consistent with the observation that MRSA strains that emerged in the community are now also being transmitted and causing disease in healthcare settings.27 28 Outbreaks of skin and soft tissue infections caused by PFT USA400 and linked to transmission in newborn nursery and postnatal ward settings have previously been described.24 29 Surveillance cultures did not identify healthcare workers colonised with the outbreak strain of MRSA in these previous investigations, and maternal colonisation cultures were not obtained.

Our investigation reveals that our newborn patients acquired MRSA infection during their stay in the hospital. The timing of onset of MRSA skin lesions before or within a limited number of days of discharge among multiple patients, along with the identification of one MRSA-colonised newborn on discharge are indicative of transmission within the facility. In addition, no common exposures or likely sources of MRSA transmission outside of the hospital were identified among the patients. Mother-to-infant transmission was considered as a potential source of transmission. S aureus is not a common cause of early-onset neonatal sepsis or other neonatal infection. However, S aureus can be present as normal vaginal flora, and previous reports have described likely vertical transmission of S aureus from the maternal genital tract to newborn infants.3033 In our investigation, vertical transmission of MRSA was not identified as a likely source of MRSA exposure. No MRSA was identified on nasal or vaginal cultures obtained from women presenting for delivery during the surveillance period, including the mothers of the two patients who had MRSA skin lesions in December 2004. This shows that MRSA colonisation is not common among peripartum women in this community. S aureus has been detected at a rate of 0–12% in the vagina during late pregnancy, consistent with our results.34

The implications of two healthcare workers being colonised with the outbreak strain of MRSA are unclear. The MRSA-colonised nurse was on duty in the nursery at the time all patients were admitted to the nursery; however, no medical records document specific interactions between the nurse and the patients. The doctor who was colonised with the outbreak strain was known to work in the nursery, but the documentation indicated her attending only one of the patients. One or both of these healthcare workers might have introduced the MRSA strain into the nursery and transmitted the organism directly to one or more of the patients, or the healthcare workers might have become colonised as a result of contact with an already colonised or infected newborn. In addition, because the same strain has been identified in outbreaks and prevalence studies in multiple states, colonisation of the healthcare workers might have been unrelated to transmission in the nursery. A high prevalence of MRSA has been reported anecdotally among children with community-associated S aureus infections examined at facilities in Chicago. Because decolonisation of the colonised healthcare workers and reinforcement of nursery infection control practices were performed concurrently, determining the relative role of each intervention in termination of the outbreak is difficult.

The majority of CA-MRSA skin infections have been described as abscesses. However, our patients presented with pustular or vesicular lesions that occurred at the same time a neonate might present with vesicular lesions resulting from herpes simplex virus infection. Therefore, MRSA should be included in the differential diagnosis of pustular or vesicular lesions that occur during the first 2 weeks of life. Furthermore, doctors should consider obtaining microbiological cultures when neonates present with skin lesions.

Nine (82%) of 11 newborns involved in this outbreak were boys. Although the role of male sex in this outbreak is unclear, male sex has been identified as a risk factor for staphylococcal colonisation and infection among newborns in previous studies.35 Because of the predominance of boys among the patients, circumcision was considered as a potential risk factor for infection; however, none of the patients had been circumcised. Nine of the 11 patients were born by caesarean delivery. Because newborns whose births are by caesarean delivery remain in the hospital longer than newborns delivered vaginally, the role of caesarean delivery in MRSA infection is unclear.

Spread of S aureus occurs from direct contact with infected or colonised body fluids or contaminated hands or inanimate objects. Therefore, strict adherence to standard infection control precautions in healthcare settings and maintenance of optimal general hygiene in community settings are essential to limiting the spread of S aureus infections.36 37 This outbreak underscores the importance of strict adherence to infection control precautions (eg, consistent hand hygiene and appropriate environmental cleaning) to prevent transmission of MRSA in the nursery.

Our investigation has some limitations. Case finding was conducted only among newborns who returned to the hospital for follow-up or treatment of skin infections. If newborns delivered at the hospital developed skin infections but sought treatment at other healthcare facilities, they would not have been identified through this investigation. Surveillance cultures of peripartum women, newborns and healthcare workers were not conducted during the height of the outbreak, only after certain control measures had been implemented. Only the nares of newborns were cultured; it is possible that additional cases may have been identified if more sites had been screened.

In conclusion, this investigation underscores the need for healthcare providers to be aware that MRSA can cause skin infections among otherwise healthy newborns and the importance of adhering to standard infection control practices. Comparison or prospective studies are needed to identify specific risk factors for and targeting measures to prevent MRSA acquisition and transmission among neonates.

Acknowledgments

We are grateful to G E Fosheim, B Jensen, S K McAllister, L K McDougal and T J Török from Centers for Disease Control and Prevention, Atlanta, Georgia, USA, R S Daum from University of Chicago Children’s Hospital, Chicago, Illinois, USA and W S Paul from Chicago Department of Public Health, Chicago, Illinois, USA, for their technical assistance.

REFERENCES

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Footnotes

  • Competing interests: None.

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