Epidemic Spread of a Single Clone of Methicillin-Resistant Staphylococcus aureus among Injection Drug Users in Zurich, Switzerland

Abstract

We describe an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) among injection drug users (IDUs). From August 1994 through December 1999, we registered 31 IDUs with MRSA infections (12 with soft-tissue infection, 7 with pneumonia [fatal in 1], 7 with endocarditis [fatal in 1], 2 with osteomyelitis, 2 with septic arthritis, and 1 with ulcerative tonsillitis), with a marked increase in the number of IDUs registered during 1998 and 1999. Of 31 patients, 15 (48%) were infected with human immunodeficiency virus. A point-prevalence study among IDUs who frequented outpatient facilities in Zurich revealed an MRSA carriage rate of 10.3% (range, 0%-28.6%) in various facilities. In all but 1 case, pulsed-field gel electrophoresis banding patterns of isolates obtained from these patients were indistinguishable from isolates of the initial 31 IDUs registered. Risk factors for MRSA carriage were disability and prior hospitalization in a hospice. In summary, MRSA became endemic in IDUs in Zurich as a result of the spread of a single clone. This clone caused major morbidity and was responsible for a lethal outcome in 2 cases.

Carriage ofStaphylococcus aureusAmong Injection Drug Users: Lower Prevalence in an Injection Heroin Maintenance Program Than in an Oral Methadone Program

“…This result is surprising considering the recent MRSA epidemic among injection drug users in the neighboring city of Zurich. 5 However, this finding mirrors the low MRSA prevalence (4%) among nosocomial S. aureus isolates in Basel, 22 and suggests that the injection drug user populations in the two cities are not in close contact. This observation also illustrates the importance of regular surveillance of the local epidemiologic situation regarding antibiotic-resistant organisms.…”

“…4 Such an outbreak recently occurred in Switzerland. 5 Colonization with S. aureus, particularly nasal carriage of S. aureus, plays a key role in the pathogenesis and increases the risk of S. aureus infection. 6,7 However, the biological mechanisms of nasal colonization by S. aureus are still unclear.…”

Staphylococcus aureus Infections in Injection Drug Users: Risk Factors and Prevention Strategies

“…Other infections associated with S. aureus in IDUs are septic arthritis, osteomyelitis, and lung abscesses. Furthermore, an association between injection drug use and MRSA [19], and even outbreaks of MRSA infections among IDUs, have been described in the United States [20] and recently in Switzerland [21,22].…”

“…Similarly, S. aureus may spread among drug users in shooting galleries, crack houses or other sites where drugs are consumed, and where hygiene is usually poor. Indeed, Craven et al [63] reported an MRSA outbreak among IDUs who frequented the same shooting gallery, and frequent and close social contacts was considered to be the most likely explanation for the epidemic spread of a single clone of MRSA among IDUs in Zurich, Switzerland [21].…”

Genetic analysis of Staphylococcus aureus from intravenous drug user lesions

“…Staphylococcus aureus is the most common cause of such infections (Lowy & Miller, 2002) and, although usually minor in nature, sequelae such as osteomyelitis and bacteraemia are not uncommon, and severe invasive diseases including infective endocarditis have been reported (Spijkerman et al, 1996). Little is known about the epidemiology of S. aureus amongst IVDUs, as modern molecular epidemiological methods have only been applied to the study of outbreaks among drug users (Fleisch et al, 2001), rather than analysing endemic strains (Lowy & Miller, 2002).…”