By Carol A. Kemper, MD, FACP, Section Editor: Updates

Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases, Santa Clara Valley Medical Center

Staphylococcus aureus Bacteremia Increased in Families

SOURCE: Oestergaard LB, Christianen MN, Schmiegelow MD, et al. Familial clustering of Staphylococcus aureus bacteremia in first-degree relatives. A Danish nationwide cohort study. Ann Intern Med 2016;165:390-398.

Animal data suggest a genetic predisposition to Staphylococcus aureus bacteremia (SAB) and infection. These authors examined whether there is an increased risk of SAB in first-degree relatives of an individual with a history of hospital-acquired or non-hospital-acquired SAB. They accessed the Danish Fertility Database for information on family relationships, cross-linking it with the Danish Civil Registration System, and the Danish Staphylococcal Bacteremia Database. This latter registry was established in 1957, and holds information on isolates collected since 2007, as well as clinical data.

An index case was defined as the first family member with the first SAB event. Non-hospital-acquired bacteremias were defined as positive blood cultures for SA obtained with the first two days of hospital admission, whereas hospital-onset SAB was defined as occurring after the first two days of hospitalization. Several Poisson regression models were used, examining the incidence ratios from 1992 to 2011, and making adjustments for demographics, such as age and sex, as well as underlying conditions like cancer, diabetes, hemodialysis status, and the presence of a prosthetic knee or hip or cardiac valve. To exclude the risk of transmission within a family, clonal lineages were examined for the available isolates.

The incidence of SAB was significantly higher in men than in women, and peaked at ages 80-85 years. The rate of SAB was more than double in first-degree relatives of an index case compared with the general population. Those at greatest risk appeared to be individuals caring for a male index case, but the risk was similar whether this was a parent or a sibling. The risks to family members were greater when the index case had non-hospital-acquired SAB than hospital-acquired SAB. No increased risk was observed in spouses of an index case. Further, 80% of the secondary cases were infected with an SA strain different from the index case.

Familial clustering of cases of SAB in first-degree relatives, due to differing S. aureus isolates, suggests an underlying familial predisposition to S. aureus infection, distinct from the risk of household transmission or colonization. Interestingly, the risks to family members appeared greatest when exposed to an index case with community-onset SAB. Although the authors made adjustments in their analyses for several important underlying diseases, the risks of SAB in those with atopy, eczema, or skin conditions do not appear to have been included as a risk factor in the analysis. Skin conditions, especially atopy and eczema, which can run in families, have been recognized as a risk factor for S. aureus colonization and infection.

Atypical Mycobacterial Infection in Cardiac Surgery Patients

SOURCE: California Department of Health. All Facilities Letter (AFL 16-14). Mycobacterium chimaera infections associated with exposure to Sorin 3T heater-cooler devices during open chest cardiac surgery. Sept. 27, 2016. Available at: http://www.cdph.ca.gov/certlic/facilities/Documents/LNC-AFL-16-14.pdf. Accessed Oct. 19, 2016.

A highly unusual atypical mycobacterial infection due to M. chimaera has been identified in cardiac surgery patients in Europe and more recently in a patient undergoing cardiac surgery in a California hospital in 2014. These cases have been linked to the use of a Sorin Group Deutschland GmbH Stockert 3TC Heater-Cooler system, used during cardiac bypass. The current belief is that units produced before August 2014, when specific cleaning and disinfection measures were instituted, were contaminated during production and are the source for these infections. These units can be found worldwide, are used in many U.S. hospitals, and may put patients at risk for infection for up to five years following surgery.

These infections first were described in patients undergoing cardiac surgery in Switzerland and Germany.1,2 Sax et al identified a total of six patients with endocarditis or vascular graft infection, which became clinically evident 1.5 to 3.6 years following surgery.1 The occurrence of two cases of this highly unusual infection in one hospital prompted an epidemiologic investigation to identify the source for the outbreak, and to look for other cases. M. chimaera was isolated from cardiac tissues, blood cultures, and other biopsy specimens. It also was isolated from the water circuits of the heater-cooler units connected to the cardiac bypass, as well as air samples taken when the units were in use. Molecular methods confirmed identical strains within two clusters.

These infections may cause sternal wound infection and osteomyelitis, endocarditis, disseminated granulomatous disease, and persistent bacteremia. The diagnosis is difficult to make for several reasons. The symptoms may not manifest until years following surgery, the detection of atypical mycobacterial infections can be missed or delayed because special culture media and techniques are required to identify the presence of infection, and the organism may be mis-identified as Mycobacterium avium complex (MAC). Identification of M. chimaera can be distinguished from MAC organisms only by the use of molecular 16S ribosomal RNA sequencing. It is considered pathogenic only rarely, and for these reasons, the infections were not recognized initially as clinically significant.

The FDA has issued warning letters to the manufacturer. The company has instituted cleaning and disinfection measures, and cultures taken from the Sorin production line in June 2015 did not show evidence of persistent infection. Therefore, only units manufactured before September 2014 appear to be at issue. Safety Communications were issued to hospitals in October 2015 and June 2016, with recommendations for proper use of the equipment, and cleaning and disinfection instructions. In addition, hospitals that use the at-risk Sorin 3TC devices are being asked to review all cardiac surgery cases for possible infection for at least the previous two years, and to notify cardiac surgeons and physicians who provide care for cardiac surgery patients, as well as infectious disease specialists, requesting they provide notification of suspect cases. In October, the Centers for Disease Control and Prevention advised that potentially exposed patients and their physicians be notified.

REFERENCES

  1. 1.Sax H, Bloemberg G, Hasse B, et al. Prolonged outbreak of Mycobacterium chimaera infection after open-chest heart surgery. Clin Infect Dis 2015;61:67-75.
  2. Haller S, Höller C, Jacobshagen A, et al. Contamination during production of heater-cooler units by Mycobacterium chimaera potential cause for invasive cardiovascular infections: Results of an outbreak investigation in Germany, April 2015 to February 2016. Euro Surveill 2016;21(17).