Outi Lyytikäinen

Trends and outcome of nosocomial and community-acquired bloodstream infections due to Staphylococcus aureus in Finland, 1995–2001

In Finland, Staphylococcus aureus bloodstream infections are caused predominantly (>99%) by methicillin-sensitive strains. In this study, laboratory-based surveillance data on Staphylococcus aureus bloodstream infections occurring in Finland from 1995 to 2001 were analyzed. Preceding hospitalizations for all persons with Staphylococcus aureus bloodstream infections were obtained from the national hospital discharge registry, and data on outcome was obtained from the national population registry. An infection was defined as nosocomial when a positive blood culture was obtained more than 2 days after hospital admission or within 2 days of admission if there was a preceding hospital discharge within 7 days. A total of 5,045 cases were identified. The annual incidence of Staphylococcus aureus bloodstream infection rose by 55%, from 11 per 100,000 population in 1995 to 17 in 2001. The increase was detected in all adult age groups, though it was most distinct in patients >74 years of age. Nosocomial infections accounted for 51% of cases, a proportion that remained unchanged. The 28-day death-to-case ratio ranged from 1% in the age group 1–14 years to 33% in patients >74 years of age. The 28-day death-to-case ratios for nosocomial and community-acquired infections were 22% and 13%, respectively, and did not change over time. The increase in incidence among elderly persons resulted in an increase in the annual rate of mortality associated with Staphylococcus aureus bloodstream infections, from 2.6 to 4.2 deaths per 100,000 population per year. Staphylococcus aureus bloodstream infections are increasing in Finland, a country with a very low prevalence of methicillin resistance. While the increase may be due in part to increased reporting, it also reflects a growing population at risk, affected by such factors as high age and/or severe comorbidity.

Impact of postdischarge surveillance on the rate of surgical site infection after orthopedic surgery.

OBJECTIVE To evaluate the impact of postdischarge surveillance on surgical site infection (SSI) rates after orthopedic surgery. SETTING Nine hospitals participating in the Finnish Hospital Infection Program. PATIENTS All patients who underwent hip or knee arthroplasty or open reduction of a femur fracture during 1999-2002. RESULTS The date of discharge was available for 11,812 procedures (90%). The median length of hospital stay was 8 days (range per hospital, 6-9 days). The overall SSI rate was 3.3% (range, 0.8%-6.4%). Of 384 SSIs detected, 216 (56%; range, 28%-90%) were detected after discharge: 93 (43%) were detected on readmission to the hospital, 73 (34%) at completion of a postdischarge questionnaire, and 23 (11%) at a follow-up visit. For 27 postdischarge SSIs (13%), the location of detection was unknown. Altogether, 32 (86%) of 37 of organ/space SSIs, 57 (80%) of 71 deep incisional SSIs, and 127 (46%) of 276 superficial incisional SSIs were detected after discharge. Most SSIs (70%) detected on readmission were severe (organ/space or deep incisional), whereas most SSIs (86%) detected at follow-up visits or at completion of a postdischarge questionnaire were superficial. Of all SSIs, 78% (range, 48%-100%) were microbiologically confirmed. Microbiologic confirmation was less common after discharge than during postoperative hospital stay (66% vs 93%; P<.001). CONCLUSIONS Postdischarge surveillance had a large impact on the rate of SSI detected after orthopedic surgery. However, postdischarge surveillance conducted by means of a questionnaire detected only a minority of deep incisional and organ/space SSIs.

Outbreak caused by two multi-resistant Acinetobacter baumannii clones in a burns unit: emergence of resistance to imipenem.

Since early 1992 an increased number of tobramycin- and imipenem-resistant Acinetobacter spp. were observed causing colonization, wound infections, and bacteraemias in a burns and plastic surgery unit. This raised the question of whether this outbreak was caused by a single or by multiple Acinetobacter spp. clones. To study this, 97 Acinetobacter spp. isolates from clinical samples from different hospital units as well as isolates from the environment and the hands of the staff were characterized by antibiogram, plasmid profile and ribotyping. Two dominant multi-resistant A. baumannii clones were identified; one of them was sensitive to polymyxin B only. There was a close correlation between the results obtained by plasmid profiling and ribotyping. No common environmental source or significant hand carriage, or spread of these strains outside the unit were detected. The burns patients were the most likely reservoir, and strain transmission occurred in spite of strict control measures.

Healthcare-associated infections in Finnish acute care hospitals: a national prevalence survey, 2005

The objectives of the first national prevalence survey on healthcare-associated infections (HAIs) in Finland were to assess the extent of HAI, distribution of HAI types, causative organisms, prevalence of predisposing factors and use of antimicrobial agents. The voluntary survey was performed during February-March 2005 in 30 hospitals, including tertiary and secondary care hospitals and 10 (25%) other acute care hospitals in the country. The overall prevalence of HAI was 8.5% (703/8234). Surgical site infection was the most common HAI (29%), followed by urinary tract infection (19%) and primary bloodstream infection or clinical sepsis (17%). HAI prevalence was higher in males, among intensive care and surgical patients, and increased with age and severity of underlying illness. The most common causative organisms, identified in 56% (398/703) of patients with HAIs, were Escherichia coli (13%), Staphylococcus aureus (10%) and Enterococcus faecalis (9%). HAIs caused by multi-resistant microbes were rare (N = 6). A total of 122 patients were treated in contact isolation due to the carriage of multi-resistant microbes. At the time of the survey, 19% of patients had a urinary catheter, 6% central venous line and 1% were ventilated. Antimicrobial treatment was given to 39% of patients. These results can be used for prioritising infection control measures and planning more detailed incidence surveillance of HAI. The survey was a useful tool to increase the awareness of HAI in participating hospitals and to train infection control staff in diagnosing HAIs.

Trends and geographical variation in invasive pneumococcal infections in Finland.

We evaluated regional variation and trends in invasive pneumococcal infections (IPI) in Finland by using data from national, population-based laboratory surveillance and number of blood and cerebrospinal fluid (CSF) cultures performed by all microbiology laboratories during 1995–2002. The overall annualized IPI incidence was 10.6/100,000 (range by region, 7.9–15.1): 9.9 for bacteraemias (range 7.3–14.2) and 0.6 for meningitis (range 0.4–1.1). The rate in children aged<5 y was 23.5/100,000. Regional pneumococcal bacteraemia rates were correlated with blood culture sampling rates (p=0.015), but meningitis rates did not correlate with CSF culture rates. During 1995–2002, the overall annual IPI rate increased by 35.1%, from 8.2 to 11.5/100,000 (p<0.001). The annual blood culturing rate increased by 29.6% (p=0.015 for the correlation with IPI rate). Temporal increase and higher regional IPI rates were significantly associated with higher blood culturing rates. Pneumococcal serotypes included in the 7- and 10-valent conjugate vaccines caused 69.8% and 85.2% of IPIs among children aged<5 y and 49.5% and 59.3% in adults, respectively. The true incidence of pneumococcal bacteraemia in Finland may be higher than previously estimated. Introduction of universal childhood pneumococcal conjugate immunization would provide substantial health benefits to Finnish children and adults.

Bacteremia among Kidney Transplant Recipients: a Case-control Study of Risk Factors and Short-term Outcomes

Kidney transplant recipients are highly susceptible to life-threatening infections, including bacteremia. To determine the risk factors for bacteremia within the first month after renal transplantation we performed a non-concurrent transplant population-based case-control study involving all 1,000 consecutively operated adult patients at Helsinki University Central Hospital in 1987-93. All patients with at least 1 positive blood culture within 31 d of transplantation were defined as cases. Control patients were drawn systematically from the transplant population with no positive blood cultures within the first 31 d post-transplant. The study included 35 cases and 123 controls. The overall rate of bacteremia in the population was 3.5%. The case patients were more likely to have been on haemodialysis prior to transplantation (71% vs. 43%, p <0.05) and to have experienced acute rejection (46% vs. 20%, p<0.05) than the controls. Local infections (46% vs. 12%, p<0.05) were also more common among case patients. In the crude analysis an additive interaction of acute rejection and haemodialysis was found, with a 10% rate of bacteremia occurring if both conditions were present. The mortality rate within 2 months of follow-up was higher among case patients than among controls (14% vs. 1%, p<0.05) and they also returned more often to dialysis (23% vs. 4%, p<0.05). Bacteremia during the immediate postoperative period might still have severe outcomes measured as allograft and patient survival at 2 months post-transplant. Further evaluation will confirm whether a lower rate of bacteremia among kidney transplantation patients can be achieved if peritoneal dialysis is preferred to haemodialysis whenever possible.Kidney transplant recipients are highly susceptible to life-threatening infections, including bacteremia. To determine the risk factors for bacteremia within the first month after renal transplantation we performed a non-concurrent transplant population-based case-control study involving all 1,000 consecutively operated adult patients at Helsinki University Central Hospital in 1987-93. All patients with at least 1 positive blood culture within 31 d of transplantation were defined as cases. Control patients were drawn systematically from the transplant population with no positive blood cultures within the first 31 d post-transplant. The study included 35 cases and 123 controls. The overall rate of bacteremia in the population was 3.5%. The case patients were more likely to have been on haemodialysis prior to transplantation (71%, vs. 43%, p < 0.05) and to have experienced acute rejection (46% vs. 20%, p < 0.05) than the controls. Local infections (46% vs. 12%, p < 0.05) were also more common among case patients. In the crude analysis an additive interaction of acute rejection and haemodialysis was found, with a 10% rate of bacteremia occurring if both conditions were present. The mortality rate within 2 months of follow-up was higher among case patients than among controls (14%, vs. 1%, p < 0.05) and they also returned more often to dialysis (23% vs. 4%, p < 0.05). Bacteremia during the immediate postoperative period might still have severe outcomes measured as allograft and patient survival at 2 months post-transplant. Further evaluation will confirm whether a lower rate of bacteremia among kidney transplantation patients can be achieved if peritoneal dialysis is preferred to haemodialysis whenever possible.

Disease burden of prosthetic joint infections after hip and knee joint replacement in Finland during 1999–2004: capture–recapture estimation

We evaluated the Finnish Hospital Infection Program (SIRO) conducting incidence surveillance for prosthetic joint infection (PJI) from 1999 to 2004. We estimated its sensitivity using capture-recapture methods and assessed the disease burden of PJIs after hip (THA) and knee (TKA) arthroplasties (N = 13 482). The following three data sources were used: SIRO, the Finnish Arthroplasty Register (FAR), and the Finnish Patient Insurance Center (FPIC), which were cross-matched, and 129 individual PJIs were identified. After adjusting for the positive predictive value of SIRO (91%) a log-linear model including an interaction term between FAR and FPIC provided an estimated PJI rate of 1.6% [95% confidence interval (CI): 1.2-2.4] for THA and 1.3% (1.1-1.6) for TKA. Sensitivity for SIRO varied from 36% to 57%. The annual disease burden was 2.1 PJIs per 100 000 population after THA and 1.5 after TKA. The true disease burden of PJIs may be heavier than the rates from national sentinel surveillance systems usually suggest.

Panton-Valentine leukocidin genes and staphylococcal chromosomal cassette mec types amongst Finnish community-acquired methicillin-resistant Staphylococcus aureus strains, 1997-1999.

Methicillin-resistant Staphylococcus aureus (MRSA) strains from Finland covering years 1997–1999 were studied for the presence of Panton-Valentine leukocidin (PVL) gene loci, and the clinically well-defined community-acquired MRSA (CA-MRSA) strains (n = 108) also for staphylococcal chromosomal cassette mec (SCCmec) and multilocus sequence types (MLST). Only a minority (12%) of the CA-MRSA strains contained the PVL gene loci and possessed genotypes formerly described as typical to CA-MRSA strains. The majority of these strains were heterogenous by MLST and pulsed-field gel electrophoresis (PFGE) analysis but, however, harboured the SCCmec cassette type IV. In conclusion, it seems doubtful to consider only molecular characteristics such as the presence of PVL genes as definite markers for CA-MRSA strains.

Cell surface properties of Acinetobacter baumannii

Cell surface properties of 78 strains of Acinetobacter baumannii of different origin (lower respiratory tract, wound, blood and environment) were investigated. The bacterial adhesion to collagen, fibronectin, fibrinogen and vitronectin was detected by particle agglutination assays. Salt aggregation tests were used to determine the cell surface hydrophobicity of isolated A. baumannii strains. We found that A. baumannii strains originating from patients with wound infection and bacteraemia showed significantly lower aggregative properties compared to respiratory and environmental strains. Electron microscopic investigations revealed more fimbriated bacterial cells among the highly aggregative A. baumannii strains. This study demonstrates that the investigated A. baumannii strains can be divided into two different groups according to their cell surface properties and source of isolation, whereas the majority of strains, from the lower respiratory tract and the hospital environment expressed strong adhesive properties.

Risk factors for death in a cohort of patients with and without healthcare-associated infections in Finnish acute care hospitals

We evaluated risk factors for death among hospitalised patients with healthcare-associated infections (HCAIs) using the McCabe classification and Charlson index to predict mortality. The study consisted of a cohort of 703 patients with HCAIs and 7531 patients without HCAI in acute care hospitals participating in the Finnish national prevalence survey in 2005. We used Centers for Disease Control and Prevention definitions for HCAIs and recorded the McCabe classification for comorbidity. We used the date from the prevalence survey and the patients national identity code in order to retrieve data from the National Hospital Discharge Registry on discharge diagnoses (International Classification of Diseases-10 codes) for the Charlson index and the dates of death from the National Population Information System. Of all inpatients, 425 (5.2%) died within 28 days from the prevalence survey date; the death rate was higher in HCAI patients than in those without HCAI (9.8% vs 4.7%, P<0.001). In the multivariate regression analysis age >65 years, intensive care, McCabe classification and Charlson index, gastrointestinal system infection and pneumonia/other lower respiratory tract infections were independent predictors for death. The survival analysis, when adjusted by McCabe class or Charlson index, showed that HCAI reduced survival only among patients without severe underlying diseases. Certain types of HCAI increased the risk of death. The McCabe classification had advantages over the Charlson index as a predictor of death, because it was easier to collect from a prevalence survey.