Staphylococcus aureus ST398, New York City and Dominican Republic

Closely related Staphylococcus aureus strains of ST398, an animal-associated strain, were identified in samples collected from humans in northern Manhattan, New York, NY, USA, and in the Dominican Republic. A large population in northern Manhattan has close ties to the Dominican Republic, suggesting international transmission.


The Study
The community-based study was conducted from 2004 through 2007 in the northern section of Manhattan, a borough of New York City. Northern Manhattan contains a large, medically underserved population that has close ties to the Dominican Republic. Participants were recruited by using random-digit dialing. Consenting persons and household members were subsequently interviewed and screened for S. aureus colonization. A total of 321 eligible households containing 914 household members participated. In 9 households, 13 participants were found to be colonized with S. aureus isolates that were SmaI resistant. Digestion with the Cfr9I, an isoschizomer of SmaI, yielded identical PFGE profi les ( Figure). Subsequent multilocus sequence typing confi rmed the ST398 identifi cation (allelic profi le 3-35-19-2-20-26-39). All strains were methicillin susceptible. A representative strain was spa-typed as type t571 (allelic profi le 8-16-2-25-2-25-34-25, eGenomics type 109); it was Panton-Valentine leukocidin negative.
Characteristics of persons colonized with ST398 were similar to those of persons in the community-based study and with northern Manhattan census characteristics (Table). The 13 isolates were from 9 different families; 1 family had 4 members colonized with ST398 at either nasal or axillary sites. The mean age of those colonized was 33.4 years; only 1 child (7 years of age) was colonized. Two persons from different families were colonized with ST398 at multiple sites, none of which were confi rmed as infections.
No household reported owning pets, although 2 reported animal contact. Of the 12 adults, 5 (41.7%) reported possible job exposure to S. aureus, including 1 who worked in a healthcare-associated fi eld. No household reported patronizing viveros, or live poultry markets, which are common in the Latino communities of northern Manhattan and the Bronx. Two households reported having children who attended day care, although none of these children were colonized with S. aureus. Although 15% of the Dominican population in the study reported travel to the Dominican Republic within 6 months of their interview, none of the colonized participants reported recent travel to the Dominican Republic. No contact among the different households was reported.
A second collection of S. aureus isolates was gathered during 2007 and 2008 from a convenience sample of 89 anonymous infection and colonization isolates received from the Dominican Republic. Six isolates were identifi ed as methicillin-susceptible S. aureus clone ST398. Strains were provided by 1 hospital in Santo Domingo, Dominican Republic (n = 53), and 1 microbiology laboratory, the Laboratorio Referencia (n = 28), which serves as a reference laboratory for the country. Four isolates from the hospital and 2 from Laboratoria Referencia were identifi ed as methicillin-susceptible ST398. Sociodemographic data on these persons were limited. Two of the ST398 isolates were from women with infections living in Santo Domingo, and the remaining 4 were colonization samples. Of the 6 isolates, 5 were found to be spa-type t571 (eGenomics type 109), and 1 was found to be type t3625 (eGenomics untyped).
Pairwise similarity scores for the isolates were calculated by the Dice coeffi cient, and an overall similarity score was calculated by using the unweighted pair group method with arithmetic mean. Comparing the isolates by using a dendrogram-based similarity score >70%, we found that the strains from northern Manhattan and from the Dominican Republic were closely related, although they contrasted with ST398 isolates from Canada (provided by Scott Weese, Ontario Veterinary College, University of Guelph) (Figure) (10).

Conclusions
Identifi cation of the S. aureus clone ST398 in northern Manhattan and in the Dominican Republic suggests its introduction into the United States by travelers between the 2 countries. The largely Latino population of northern Manhattan is composed mainly of immigrants or fi rst-generation families from the Dominican Republic; travel between the 2 regions is common. Alternatively, northern Manhattan may contain reservoirs, such as live poultry markets, which may serve as a means of strain transmission.
Colonization or infection with the S. aureus clone ST398 has been associated with exposure to pigs, pets, and other animals (5,(7)(8)(9), and the S. aureus clone ST398 has been isolated from meat products (2). However, transmission is not limited to animal exposures. Person-to-person spread has occurred among household members and in the hospital setting (6,8,11). For example, a dramatic increase in persons colonized as well as infected with MRSA clone ST398 was recently reported in a Dutch hospital (12).
The presence of this strain among several household members in our study reinforces earlier observations of the potential for horizontal transmission of this clone after it is introduced into an appropriate setting. Although information about the persons from the Dominican Republic was limited, the 2 groups provided identical strain profi les, suggesting a possible link between the 2 countries. Given ST398's history of rapid dissemination in the Netherlands, its potential for the acquisition of methicillin resistance, and its ability to cause infections in both community and hospital settings, monitoring the prevalence of this strain in northern Manhattan and the Dominican Republic will be important to understand more about its virulence and its ability to spread in these communities.