New methods to investigate infectious disease transmission and pathogenesis--Staphylococcus aureus disease in drug users

Pelvic and acetabular fracture management in intravenous drug users

INTRODUCTION

Pelvic and acetabular fractures are significant injuries associated with high morbidity or mortality. Intravenous drug users (IVDU) represent a challenging group of patients, with an increased risk of complications and infection. To our knowledge there has not been any published literature concerning IVDU and this type of injuries.

PATIENTS AND METHODS

A group of 19 patients with a history of IVDU and who had sustained an injury were identified.

RESULTS

The mean age at injury was 36 years old; nine had a pelvic fracture and ten had an acetabular fracture. No complications were observed in the pelvic group. In the acetabular group, the infection risk was 50% and the risk of femoral head avascular necrosis was 33%. The mean follow up was 43.1 months from injury.

CONCLUSION

We advise emphasis in the high infection and avascular necrosis rates, when consenting the patient for an operation. Furthermore, non-operative treatment should be considered, where possible.

LEVEL OF EVIDENCE

Level III. Retrospective cohort study. Prognostic-investigating the effect of a patient characteristic on the outcome of the disease.

Insights into the epidemiology of methicillin-resistant coagulase-negative Staphylococci carriage in community-based drug users

BACKGROUND

Coagulase-negative Staphylococci (CoNS) are opportunistic pathogens. Methicillin-resistant CoNS (MRCoNS) remain a major cause of nosocomial infections, but limited information is available in communities. We, therefore, aimed to investigate the epidemiology of CoNS nasal carriage, especially MRCoNS in community-based drug users.

METHODS

Drug users were included in the cross-sectional study from three communities in Guangzhou, China. A face-to-face questionnaire was used to collect individual information and nasal swabs were collected to identify CoNS and MRCoNS isolates. Phenotypic and genotypic characterization of MRCoNS isolates were detected by using the disk diffusion method and polymerase chain reaction assays. Factors impacting MRCoNS carriage were assessed and estimated odds ratios (ORs) and 95% confidence intervals (CIs) by using logistic regression models.

RESULTS

Overall, 353 drug users were eligible and included in the study. The prevalence of CoNS and MRCoNS were 42.78% and 29.18%, respectively. Having a history of being in prison (aOR = 2.16, 95% CI: 1.10-4.22) and a history of heroin snorting in the past 6 months (aOR = 1.87, 95% CI: 1.14-3.05) were risk factors for MRCoNS nasal carriage in drug users. The proportions of multidrug resistance for CoNS and MRCoNS isolates were respectively 54.38% and 66.07%. The predominant multidrug resistance pattern for CoNS and MRCoNS isolates was simultaneously non-susceptible to penicillin, cefoxitin and trimethoprim-sulfamethoxazole. MRCoNS isolates that were positive for erythromycin- (χ² = 15.49, P < 0.001), tetracycline- (χ² = 44.88, P < 0.001), penicillin- (χ² = 3.86, P = 0.049), clindamycin- (χ² = 4.18, P = 0.028), and gentamicin- (χ² = 20.66, P < 0.001) resistance genes had significantly higher rates of resistance to corresponding antibiotics.

CONCLUSIONS

The prevalence of MRCoNS nasal carriage was high in community-based drug users. Drug users with risk factors should be paid greater attention to. The use of antibiotics in drug users needs further investigation and control.

Impact of Mobility on Methicillin-Resistant Staphylococcus aureus among Injection Drug Users

In this study, we develop and present a deterministic model for the transmission dynamics of methicillin-resistant staphylococcus aureus (MRSA) among injection drug users. The model consists of non-injection drug users as well as low-and high-risk injection drug users (IDUs). The model further incorporates the movement of these individuals between large metro, suburban and rural areas. The model parameters were estimated by fitting the model to the 2008-2013 disease prevalence data for non-IDUs obtained from the Agency for Healthcare and Research and Quality (AHRQ), as well as the 2009-2013 Census Bureau data for the number of individuals migrating between three different counties in Kansas. Sensitivity analysis was implemented to determine the parameters with the most significant impact on the total number of infected individuals; the transmission probability, recovery rates, and positive behavioral change parameter for the subgroup have the most significant effect on the number of infected individuals. Furthermore, the sensitivity of the parameters in the different areas was the same when the areas are disconnected. When the areas are connected, the parameters in large-metro areas were the most sensitive, and the rural areas were least sensitive. The result shows that to effectively control the disease across the large metro, suburban and rural areas, it is best to focus on controlling both behavior and disease in the large metro area as this has a trickle-down effect to the other places. However, controlling behavior and disease at the same time in all the areas will lead to the elimination of the disease.

Social Influence in Liver Fluke Transmission: Application of Social Network Analysis of Food Sharing in Thai Isaan Culture

In northeastern Thai (Isaan) culture traditional raw fish dishes and raw fish-eating habits are common. Eating and sharing meals together among the community's members, especially relatives and neighbours, are a common practice in both daily life and social gathering events. Fish are a significant protein source and are associated with variety of traditional recipes. Cyprinid fish are one of the most preferred fish by Isaan villagers for daily consumption because they are accessible and affordable. Consumption of these fish probably causes the persistence of high endemicity of human liver fluke infection, particularly with Opisthorchis viverrini, in northeast Thailand. Because the consumption of raw cyprinid fish is a well-documented risk factor for liver fluke infection, sharing of risky raw fish dishes may influence disease transmission through a community. Social network analysis was used to investigate fish and fish-based meal sharing among household members in Isaan villages in liver fluke endemic areas. The findings from three studies confirmed the persistence of traditional Isaan raw fish consumption and food-sharing practice. Social connections via food sharing among villagers played an important role in liver fluke infection and transmission dynamics as a risk factor. Thus these sociocultural factors should be taken into account in designing strategies for control of opisthorchiasis and other food-borne illnesses at the community level.

Transmission dynamics for Methicilin-resistant Staphalococous areus with injection drug user

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterial pathogen resistance to antibiotics including methicillin. The resistance first emerged in 1960 in a healthcare setting only after two years of using methicillin as a viable treatment for methicillin-susceptible Staphylococcus aureus. MRSA leads to infections in different parts of the body including the skin, bloodstream, lungs, or the urinary tract.

Methods

A deterministic model for methicillin-resistant Staphylococcus aureus (MRSA) with injection drug users is designed. The model incorporates transmission of MRSA among non-injection drug users and injection drug users (IDUs) who are both low-and high-risk users. A reduced MRSA transmission model with only non-IDUs is fitted to a 2008-2013 MRSA data from the Agency for Healthcare and Research and Quality (AHRQ). The parameter estimates obtained are projected onto the parameters for the low-and high-risk IDUs subgroups using risk factors obtained by constructing a risk assessment ethogram. Sensitivity analysis is carried out to determine parameters with the greatest impact on the reproduction number using the reduced non-IDUs model. Change in risk associated behaviors was studied using the full MRSA transmission model via the increase in risky behaviors and enrollment into rehabilitation programs or clean needle exchange programs. Three control effectiveness levels determined from the sensitivity analysis were used to study control of disease translation within the subgroups.

Results

The sensitivity analysis indicates that the transmission probability and recovery rates within the subgroup have the highest impact on the reproduction number of the reduced non-IDU model. Change in risk associated behaviors from non-IDUs to low-and high-risk IDUs lead to more MRSA cases among the subgroups. However, when more IDUs enroll into rehabilitation programs or clean needle exchange programs, there was a reduction in the number of MRSA cases in the community. Furthermore, MRSA burden within the subgroups can effectively be curtailed in the community by implementing moderate- and high-effectiveness control strategies.

Conclusions

MRSA burden can be curtailed among and within non-injection drug users and both low-and high-risk injection drug users by encouraging positive change in behaviors and by moderate- and high-effectiveness control strategies that effectively targets the transmission probability and recovery rates within the subgroups in the community.

Staphylococcus aureus bacteraemia and endocarditis - epidemiology and outcome: a review

PURPOSE

To review the epidemiology of Staphylococcus aureus bacteraemia (SAB) and endocarditis (SAE), and discuss the short- and long-term outcome.  Materials and methods: A literature review of the epidemiology of SAB and SAE.

RESULTS

The reported incidence of SAB in Western countries is 16-41/100,000 person-years. Increasing incidence has been observed in many regions, in Iceland by 27% during 1995-2008. The increase is believed to depend on changes in population risk factors and possibly better and more frequent utilization of diagnostic procedures. S. aureus is now the leading causes of infective endocarditis (IE) in many regions of the world. It accounts for 15-40% of all IE cases, and the majority of cases in people who inject drugs (PWID). Recently, the incidence of SAE in PWID in Stockholm, Sweden, was found to be 2.5/1000 person-years, with an in-hospital mortality of 2.5% in PWID as compared to 15% in non-drug users. The 30-day mortality associated with SAB amounts to 15-25% among adults in Western countries, but is lower in children (0-9%). Mortality associated with SAE is high (generally 20-30% in-hospital mortality), and symptomatic cerebral embolizations are common (12-35%). The 1-year mortality reported after SAB and SAE is 19-62% and reflects deaths from underlying diseases and complications caused by the infection. In a subset of SAE cases, valvular heart surgery is needed (15-45%), but active intravenous drug use seems to be a reason to refrain from surgery. Despite its importance, there are insufficient data on the optimal management of SAB and SAE, especially on the required duration of antibiotic therapy.  Conclusions: The epidemiology of SAB and SAE has been changing in the past decades. They still carry a substantial morbidity and mortality. Intensified studies on treatment are warranted for improving patient outcome.

Social network analysis of food sharing among households in opisthorchiasis endemic villages of Lawa Lake, Thailand

Consumption of raw fish is a well-documented risk factor for Opisthorchis viverrini infection. Sharing of food, especially raw fish recipes may influence the spread of disease through a community. Using social network analysis of an ego network, we investigated food sharing among households in an Opisthorchis-endemic area. Network centrality properties were used to explain the differences in O. viverrini transmission and control between villages with a low and high prevalence of infection. Information on demography and O. viverrini infection in 2008 from villagers in the Lawa Lake area was extracted from the Tropical Disease Research Center database. The two villages that had the lowest and the highest O. viverrini infection at the household level were recruited. Ten percent of households of each village were randomly sampled. Participatory epidemiology and face-to-face structured interviews guided by a social network questionnaire were used to collect data on livelihood, agricultural patterns, food sources, raw fish eating habits, and other food sharing during daily life and social gatherings. The number of contacts including in-degree and out-degree varied from 0 to 7 in the low-infection village and 0 to 4 in the high-infection village. The mean number of contacts for the food-sharing network among the low- and high-infection villages was 1.64 and 0.73 contacts per household, respectively. Between these villages, the mean number of out-degree (p=0.0125), but not in-degree (p=0.065), was significantly different. Food-sharing differed in numbers of sharing-in and sharing-out between the two villages. Network analysis of food sharing may be of value in designing strategies for opisthorchiasis control at the community level.

Dual Recognition Strategy for Specific and Sensitive Detection of Bacteria Using Aptamer-Coated Magnetic Beads and Antibiotic-Capped Gold Nanoclusters

Food poisoning and infectious diseases caused by pathogenic bacteria such as Staphylococcus aureus (SA) are serious public health concerns. A method of specific, sensitive, and rapid detection of such bacteria is essential and important. This study presents a strategy that combines aptamer and antibiotic-based dual recognition units with magnetic enrichment and fluorescent detection to achieve specific and sensitive quantification of SA in authentic specimens and in the presence of much higher concentrations of other bacteria. Aptamer-coated magnetic beads (Apt-MB) were employed for specific capture of SA. Vancomycin-stabilized fluorescent gold nanoclusters (AuNCs@Van) were prepared by a simple one-step process and used for sensitive quantification of SA in the range of 32-10(8) cfu/mL with the detection limit of 16 cfu/mL via a fluorescence intensity measurement. And using this strategy, about 70 cfu/mL of SA in complex samples (containing 3 × 10(8) cfu/mL of other different contaminated bacteria) could be successfully detected. In comparison to prior studies, the developed strategy here not only simplifies the preparation procedure of the fluorescent probes (AuNCs@Van) to a great extent but also could sensitively quantify SA in the presence of much higher concentrations of other bacteria directly with good accuracy. Moreover, the aptamer and antibiotic used in this strategy are much less expensive and widely available compared to common-used antibodies, making it cost-effective. This general aptamer- and antibiotic-based dual recognition strategy, combined with magnetic enrichment and fluorescent detection of trace bacteria, shows great potential application in monitoring bacterial food contamination and infectious diseases.

Not in the vein: 'missed hits', subcutaneous and intramuscular injections and associated harms among people who inject psychoactive drugs in Bristol, United Kingdom

BACKGROUND

The extent of intentional or accidental subcutaneous and intramuscular injections and the factors associated with these have rarely been studied among people who inject drugs, yet these may play an important role in the acquisition bacterial infections. This study describes the extent of these, and in particular the factors and harms associated with accidental subcutaneous and intramuscular injections (i.e. 'missed hits').

METHODS

People who inject drugs were recruited using respondent driven sampling. Weighted data was examined using bivariate analyses and logistic regression.

RESULTS

The participants mean age was 33 years (31% aged under 30-years), 28% were women, and the mean time since first injection was 12 years (N=329). During the preceding three months, 97% had injected heroin, 71% crack-cocaine, and 16% amphetamines; 36% injected daily. Overall, 99% (325) reported that they aimed to inject intravenously; only three aimed to inject subcutaneously and one intramuscularly. Of those that aimed to inject intravenously, 56% (181) reported ever missing a vein (for 51 this occurred more than four times month on average). Factors associated with 'missed hits' suggested that these were the consequence of poor vascular access, injection technique and/or hygiene. 'Missed hits' were twice as common among those reporting sores/open wounds, abscesses, or redness, swelling and tenderness at injection sites.

CONCLUSION

Intentional subcutaneous and intramuscular injections are rare in this sample. 'Missed hits' are common and appear to be associated with poor injection practice. Interventions are required to reduce risk through improving injecting practice and hygiene.

Outcomes Following Primary Total Hip or Knee Arthroplasty in Substance Misusers

The influence of drug misuse on outcomes following primary total hip (THA) or knee (TKA) arthroplasty is poorly understood. The National Hospital Discharge Survey was used to identify patients who underwent primary THA or TKA between 1990 and 2007. Patients were divided into two groups: 1) those with a diagnosis of drug misuse (cannabis, opioids, cocaine, amphetamines, sedatives, inhalants or mixed combinations) (n=13,163) and 2) those with no diagnosis of misuse (n=8,366,327). Patients with a diagnosis of drug misuse had longer hospital stays (P<0.001), nearly eight times the odds of leaving against medical advice (P<0.001) and five times the mortality rate (P<0.001). Drug misuse was associated with higher odds (P<0.001) of complications including postoperative infection, anemia, convulsions, osteomyelitis, and blood transfusion.

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

Objectives:

To compare the prevalence ofStaphylococcus aureusand methicillin-resistantS. aureus(MRSA) carriage among injection drug users (IDUs) treated in an injection heroin maintenance program with that among IDUs treated in an oral methadone program, and to determine predictors ofS. aureuscarriage.

Design:

Survey.

Setting:

Two opiate maintenance programs at a psychiatrie university clinic.

Participants:

A volunteer sample consisting of 94 (74%) of 127 IDUs treated in an injection opiate maintenance program with at least twice daily injections of heroin, and 70 (56%) of 125 IDUs treated in an oral methadone program.

Results:

Addicts treated in the intravenous heroin substitution program had a significantly lower overall rate ofS. aureuscarriage (37 of 94 [39.4%] vs 42 of 70 [60%];P= .009) and a significantly lower rate of nasal carriage (21 of 94 [22.3%] vs 30 of 70 [42.9%];P= .005) than did addicts treated in the oral methadone program. Being treated in the oral methadone program was the only independent predictor ofS. aureuscarriage (odds ratio, 2.27; 95% confidence interval, 1.19-4.31;P=.012). AllS. aureusisolates were susceptible to oxacillin.

Conclusions:

The regular use of needles under aseptic conditions did not increase the rate ofS. aureuscarriage among IDUs. Further studies are necessary to investigate whether the lower rate ofS. aureuscarriage among IDUs treated with intravenous heroin leads to a lower incidence ofS. aureusinfections in these patients.

Visualization and analytics tools for infectious disease epidemiology: a systematic review

BACKGROUND

A myriad of new tools and algorithms have been developed to help public health professionals analyze and visualize the complex data used in infectious disease control. To better understand approaches to meet these users' information needs, we conducted a systematic literature review focused on the landscape of infectious disease visualization tools for public health professionals, with a special emphasis on geographic information systems (GIS), molecular epidemiology, and social network analysis. The objectives of this review are to: (1) identify public health user needs and preferences for infectious disease information visualization tools; (2) identify existing infectious disease information visualization tools and characterize their architecture and features; (3) identify commonalities among approaches applied to different data types; and (4) describe tool usability evaluation efforts and barriers to the adoption of such tools.

METHODS

We identified articles published in English from January 1, 1980 to June 30, 2013 from five bibliographic databases. Articles with a primary focus on infectious disease visualization tools, needs of public health users, or usability of information visualizations were included in the review.

RESULTS

A total of 88 articles met our inclusion criteria. Users were found to have diverse needs, preferences and uses for infectious disease visualization tools, and the existing tools are correspondingly diverse. The architecture of the tools was inconsistently described, and few tools in the review discussed the incorporation of usability studies or plans for dissemination. Many studies identified concerns regarding data sharing, confidentiality and quality. Existing tools offer a range of features and functions that allow users to explore, analyze, and visualize their data, but the tools are often for siloed applications. Commonly cited barriers to widespread adoption included lack of organizational support, access issues, and misconceptions about tool use.

DISCUSSION AND CONCLUSION

As the volume and complexity of infectious disease data increases, public health professionals must synthesize highly disparate data to facilitate communication with the public and inform decisions regarding measures to protect the public's health. Our review identified several themes: consideration of users' needs, preferences, and computer literacy; integration of tools into routine workflow; complications associated with understanding and use of visualizations; and the role of user trust and organizational support in the adoption of these tools. Interoperability also emerged as a prominent theme, highlighting challenges associated with the increasingly collaborative and interdisciplinary nature of infectious disease control and prevention. Future work should address methods for representing uncertainty and missing data to avoid misleading users as well as strategies to minimize cognitive overload.

Total hip replacement in patients with history of illicit injecting drug use

BACKGROUND

A history of illicit injecting drug use makes indication of total hip arthroplasty (THA) in patients with end stage hip osteoarthritis difficult, as the risk of infection with colonized strains is multiplied if the patient continues to inject or inhale illicit drugs.

METHODS

A retrospective survivorship analysis of a consecutive series of 27 THA in patients with a history of illicit drug use was performed. Follow-up evaluation consisted of (1) a WOMAC score, (2) a standardized interview including queries on drug habits and eventual additional medico-surgical treatments of the affected hip, (3) a clinical examination in order to complete a Harris Hip Score, (4) radiological examination and (5) blood tests (blood sedimentation rates and C-reactive protein). Defined endpoints were death, implant revised or awaiting revision for deep infection or any other reason and lost to follow-up or follow-up after at least 2 years.

RESULTS

Overall, 5- and 10-year implant survival rates with failure for any reason were 61 % (CI: 41;81) and 52.3 % (CI: 29;76) and for septic reasons 70.6 % (CI: 52;89) and 60.5 % (CI: 36;85), respectively. Even if at the time of THA all patients and respective health care professionals confirmed abstinence of illicit injecting drug use, five patients reported occasional use. Declared abstinence of less than 1 year before THA was associated with higher recurrence rates (p = 0.001) and both with higher septic failure rates (p = 0.023, p = 0.061). Positive serology for human deficiency virus did not increase implant failure rates.

CONCLUSION

We use this unacceptable high failure rate as evidence when counseling patients and their health care professionals about the appropriate treatment of osteoarthritis in patients with a history of illicit drug use. Furthermore, we support the request of hair analysis for drugs documenting abstinence of at least 1 year before indicating THA.

Prevalence of USA300 colonization or infection and associated variables during an outbreak of community-associated methicillin-resistant Staphylococcus aureus in a marginalized urban population

BACKGROUND

In 2004, an outbreak of the USA300 strain of methicillin-resistant Staphylococcus aureus (MRSA) was identified in persons with histories of homelessness, illicit drug use or incarceration in the Calgary Health Region (Calgary, Alberta). A prevalence study was conducted to test the hypotheses for factors associated with USA300 colonization or infection.

METHODS

Participants were recruited at sites accessed by this marginalized population. Health care staff administered a questionnaire and collected crack pipes and nasal, axillary and skin infection swabs. Pipes and swabs were cultured according to standard techniques. MRSA isolates were further characterized by polymerase chain reaction (mecA, Panton-Valentine leukocidin and Staphylococcal cassette chromosome mec) and typing methods (pulsed-field gel electrophoresis, staphylococcal protein A typing and multilocus sequence typing). Colonization or infection was determined by having any one of nasal, axillary, skin infection or pipe swabs positive for USA300. Colonized participants had one or more nasal, axillary or pipe swab positive for USA300; infected participants had one or more skin infection swab positive for USA300.

RESULTS

The prevalence of USA300 colonization or infection among 271 participants was 5.5% (range 3.1% to 9.0%). USA300 cases were more likely to report manipulation of skin infections (OR 9.55; 95% CI 2.74 to 33.26); use of crack pipes was not significant despite identification of the USA300 strain on two of four crack pipes tested. USA300 cases were more likely to report drug use between sex trade workers and clients (OR 5.86; 95% CI 1.63 to 21.00), and with casual sex partners (OR 5.40; 95% CI 1.64 to 17.78).

CONCLUSION

Ongoing efforts to promote the appropriate treatment of skin infections in this population are warranted. The association of USA300 colonization or infection and drug use with sexual partners suggest a role for sexual transmission of the USA300 strain of MRSA.

Shooting up: the interface of microbial infections and drug abuse

Illicit drug control has been on the global agenda for more than a century. Infections have long been recognized as one of the most serious complications of drug abuse. Drug users are susceptible to pulmonary, endovascular, skin and soft tissue, bone and joint, and sexually transmitted infections caused by a wide range of bacterial, viral, fungal and protozoal pathogens. In addition, injection drug users are at increased risk for parenterally acquired infections such as human immunodeficiency virus, hepatitis B virus, hepatitis C virus, tetanus and malaria. Factors related to drug use, such as unsterile injection practices, contaminated drug paraphernalia and drug adulterants, increase the exposure to microbial pathogens. Illicit drugs also affect several components of the complex immune system and thus modulate host immunity. In addition, lifestyle practices such as multiple sexual partners, overcrowded housing arrangements and malnutrition serve as co-factors in increasing the risk of infection. In this review we present an overview of the unique aspects of microbial pathogenesis, immune modulation and common infections associated with drug use. We have restricted the definition of drug abuse to the use of illegal drugs (such as opiates, marijuana, cocaine, heroin and amphetamines), not including alcohol and nicotine.

Characterization of infecting strains and superantigen-neutralizing antibodies in Staphylococcus aureus bacteremia

Staphylococcus aureus superantigens (SAgs) are highly potent T cell mitogens. Antibodies against non-enterotoxin gene cluster (non-egc) SAgs are common in healthy adults, whereas neutralizing antibodies against egc SAgs are rare. We investigated the infecting S. aureus strains and the anti-SAg antibody response during S. aureus bacteremia (SAB). This prospective clinical study (www.clinicaltrials.gov, NCT00548002) included 43 injection drug users (IDUs) and 44 group-matched nonaddicts with SAB. spa genotypes and SAg gene patterns (multiplex PCR) of the S. aureus isolates were determined. The neutralizing capacities of sera obtained at the acute phase and the convalescent phase of SAB were tested against the SAg cocktail of the respective infecting strain and a panel of recombinant SAgs. The lineages CC59 and CC30 were more prevalent among bacteremia strains from IDUs than among strains from nonaddicts. SAg gene patterns in isolates from IDUs and nonaddicts were similar. At the acute phase of bacteremia, IDUs had more neutralizing antibodies against non-egc SAgs than did nonaddicts. Antibody titers frequently increased during infection. In contrast, there were no neutralizing antibodies against egc SAgs at disease onset and such antibodies were not induced by SAB. SAB triggers an antibody response only against non-egc SAgs. Preimmunization in IDU patients is probably due to previous exposure to the infecting strain.

Injecting-related injury and disease among clients of a supervised injecting facility

BACKGROUND

The process of drug injection may give rise to vascular and soft tissue injuries and infections. The social and physical environments in which drugs are injected play a significant role in these and other morbidities. Supervised injecting facilities (SIFs) seek to address such issues associated with public injecting drug use.

AIMS

Estimate lifetime prevalence of injecting-related problems, injury and disease and explore the socio-demographic and behavioral characteristics associated with the more serious complications.

DESIGN, SETTING, PARTICIPANTS

Self-report data from 9552 injecting drug users (IDUs) registering to use the Sydney Medically Supervised Injecting Centre (MSIC).

FINDINGS

Lifetime history of either injecting-related problems (IRP) or injecting-related injury and disease (IRID) was reported by 29% of the 9552 IDUs; 26% (n=2469) reported ever experiencing IRP and 10% (n=972) reported IRID. Prevalence of IRP included difficulties finding a vein (18%), prominent scarring or bruising (14%) and swelling of hands or feet (7%). Prevalence of IRID included abscesses or skin infection (6%), thrombosis (4%), septicaemia (2%) and endocarditis (1%). Females, those who mainly injected drugs other than heroin, and those who reported a history of drug treatment, drug overdose, and/or sex work, were more likely to report lifetime IRID. Frequency and duration of injecting, recent public injecting, and sharing of needles and/or syringes were also independently associated with IRID.

CONCLUSIONS

IRPs and IRIDs were common. Findings support the imperative for education and prevention activities to reduce the severity and burden of these preventable injecting outcomes. Through provision of hygienic environments and advice on venous access, safer injecting techniques and wound care, SIFs have the potential to address a number of risk factors for IRID.

Raising the level of analysis of food-borne outbreaks: food-sharing networks in rural coastal Ecuador

OBJECTIVES

Consuming contaminated food is a well-documented individual-level risk factor for diarrheal disease. The sharing of food also influences the distribution of diarrheal disease risk through a community and region. Understanding this social process at a population level is therefore an important dimension of risk not captured by standard individual-level analyses. We examined social networks related to food-sharing in rural villages at 2 scales: within a village, examining whether connections within these networks clustered or were uniformly spread; and among villages, looking at whether food-sharing networks differed according to the village's remoteness from a population center.

METHODS

We surveyed 2129 individuals aged 13 years and older in 2003-2004, within a representative (block-randomized) sample of 21 rural villages in Esmeraldas province, northern coastal Ecuador. We calculated degree (number of social contacts) for a social network defined by sharing food.

RESULTS

Networks of households sharing food differ according to remoteness from a metropolitan center. On average, residents living in "far villages" had 2 more social contacts than those in "close villages," and 12 more years of residence in their village. Estimates of transmissibility (a measure of outbreak potential) based on network structure varied as much as 2-fold across these villages.

CONCLUSIONS

Food-sharing practices link particular households in rural villages and have implications for the spread of food-borne pathogens. The food-sharing networks in remote rural villages are heterogeneous and clustered, consistent with contemporary theories about disease transmitters. Network-based measures may offer tools for predicting patterns of disease outbreaks, as well as guidance for interventions.

Methicillin-sensitive Staphylococcus aureus bacteraemia and endocarditis among injection drug users and nonaddicts: host factors, microbiological and serological characteristics

BACKGROUND

Endocarditis has been associated with lower mortality and fewer complications among injection drug users (IDUs) than nonaddicts in Staphylococcus aureus bacteraemia (SAB). The better prognosis of IDUs has not been clarified but it has generally been explained by younger age and other host factors. In this study, bacterial strains, their virulence factors, and host immune responses were compared among IDUs and nonaddicts with SAB, including those with and without endocarditis.

METHODS

A total of 430 consecutive adult patients with methicillin-sensitive SAB were followed prospectively for 3 months. All 44 IDUs were included, and 44 nonaddicts as controls for them. According to the modified Duke criteria, 20 patients in both groups had endocarditis. For each addict without endocarditis, an age and sex matched nonaddict was selected as a control. S. aureus isolates were assigned a genotype by PFGE, Panton-Valentine leukocidin (PVL), staphylokinase (SAK), protease, and haemolysin production. Acute and convalescent sera were tested for antibodies to alpha-haemolysin (ASTA) and teichoic acid (TAA).

RESULTS

There were no differences between IDUs and nonaddicts with SAB in the proportion of patients with a deep infection (98% vs 86%, P=0.06) or a thromboembolic complication (30% vs 14%, P=0.12). Endocarditis among IDUs was not associated with any specific strains, and only the FIN-4 strain was observed more often in IDUs than in nonaddicts (21% vs 5%, P=0.03). The majority of isolates (98%) were PVL negative, and there were no differences in the numbers of SAK, protease and haemolysin production among strains between IDUs and nonaddicts. However, haemolytic properties were found more frequently in strains from IDUs without endocarditis than those with endocarditis (88% vs 47%, P=0.007). IDUs displayed more often elevated TAA titers than nonaddicts, especially in endocarditis at acute phase (33% vs 5%, P=0.04) and at convalescent phase (50% vs 10%, P=0.01). The ASTA titer was more frequently initially positive among IDUs without endocarditis than with endocarditis (44% vs 6%, P=0.01).

CONCLUSIONS

Characterization of the bacterial strains and their virulence factors, and host immune responses did not reveal significant differences between IDUs and nonaddicts with similar clinical picture of SAB. Serological tests were not helpful in identifying patients with endocarditis.

Update on the epidemiology and management of Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus, in patients with cystic fibrosis

PURPOSE OF REVIEW

Staphylococcus aureus is one of the first and most common pathogens to be isolated from the respiratory tract of patients with cystic fibrosis. The prevalence of respiratory tract colonization/infection with both methicillin-susceptible and methicillin-resistant S. aureus has increased over the past decade. The clinical significance of colonization/infection with these pathogens is variable, leading to numerous therapeutic strategies: primary prophylaxis, eradication, treatment of cystic fiboris pulmonary exacerbations, and treatment of methicillin-resistant S. aureus.

RECENT FINDINGS

Studies have demonstrated increased prevalence of S. aureus in clinical laboratories that use selective media. Additionally, small colony variant S. aureus has been associated with persistent infection, co-infection with Pseudomonas aeruginosa, and frequent courses of antibiotics, but this phenotype may be difficult to identify in clinical laboratories. Increased prevalence of methicillin-resistant S. aureus has led to use of oral and inhaled antibiotics in attempts to eradicate this pathogen; these studies have yielded variable results.

SUMMARY

The epidemiology of S. aureus in cystic fibrosis has changed. Studies are needed to assess the clinical significance of the increased prevalence of both methicillin-susceptible and methicillin-resistant S. aureus, and whether primary prophylaxis or new treatment/eradication protocols are effective.

Incidence and persistence of Staphylococcus aureus nasal colonization in a community sample of HIV-infected and -uninfected drug users

A longitudinal study of 282 community-based drug users was conducted from February 1999 through September 2000. Both the incidence (15.0 cases per 100 person-years at risk; 95% confidence interval, 10.2-20.7 cases per 100 person-years at risk) and persistence of Staphylococcus aureus carriage were increased among human immunodeficiency virus (HIV)-seropositive individuals.

Meticillin-resistant Staphylococcus aureus among US prisoners and military personnel: review and recommendations for future studies

We reviewed published work examining the prevalence and risk factors for meticillin-resistant Staphylococcus aureus (MRSA) infection in two high-risk groups: prisoners and military enlistees. Significant risk factors for infection included prison occupation, gender, comorbidities, prior skin infection, and previous antibiotic use. Although characteristics such as hygiene, physical contact, and crowding were postulated as risk factors for MRSA infection, there were few epidemiological studies supporting these factors. Most studies identified were retrospective in design and only one study used prospective surveillance for MRSA colonisation among all individuals residing within a single military setting. Our results suggest that there is a high incidence of MRSA infection among individuals in prisons and military settings, but surveys that quantify the prevalence of MRSA colonisation among individuals living within these specialised settings are needed. A thorough examination of MRSA acquisition and transmission patterns in prisons and military settings could help elucidate preventive strategies in other crowded and closed settings.

The role of institutional epidemiologic weight in guiding infection surveillance and control in community and hospital populations

BACKGROUND

Institutions such as hospitals, prisons, and long-term care facilities have been identified as focal points for the transmission of emerging infections. Cost-effective control of these infections in large populations requires the identification of optimal subpopulations for targeted infection control interventions. Our objective was to quantify and compare the relative impact that individual institutions or subpopulations have on wider population-level outbreaks of emerging pathogens.

DESIGN

We describe a simple mathematical model to compute the epidemiologic weight (EW) of an institution or subpopulation. The EW represents the rate at which newly infectious individuals exit the institution under consideration.

SETTING

A hypothetical academic tertiary-care hospital (700 beds, 5-day length of stay [LOS]) and prison (3098 inmates, 27-day LOS).

PATIENTS

Individuals entering a hospital in-patient prison ward and nonprisoners entering both medical and surgical intensive-care units and those admitted to the general medical and surgical wards.

RESULTS

The recent example of the community-acquired methicillin-resistant Staphylococcus aureus epidemic is used to illustrate the EW calculation. Hospitals and prisons, which often have vastly dissimilar populations sizes and LOSs and might have differing transmission rates, can have comparable EWs and thus contribute equally to an epidemic in the community.

CONCLUSIONS

This method highlights the importance of measuring entrance and exit colonization prevalences for the optimal targeting of prevention measures. The EW not only identified superspreader institutions but also ranks them, enabling public health workers to optimize the allocation of resources to places where they are likely to be of most benefit.

Antimicrobial-resistant bacteria in the community setting

Over the past decade, antimicrobial resistance has emerged as a major public-health crisis. Common bacterial pathogens in the community such as Streptococcus pneumoniae have become progressively more resistant to traditional antibiotics. Salmonella strains are beginning to show resistance to crucial fluoroquinolone drugs. Community outbreaks caused by a resistant form of Staphylococcus aureus, known as community-associated meticillin (formerly methicillin)-resistant Staphylococcus aureus, have caused serious morbidity and even deaths in previously healthy children and adults. To decrease the spread of such antimicrobial-resistant pathogens in the community, a greater understanding of their means of emergence and survival is needed.

Genetic analysis of Staphylococcus aureus from intravenous drug user lesions

Multilocus sequence typing (MLST) of 48 methicillin-sensitive Staphylococcus aureus isolates from intravenous drug user abscesses/soft-tissue infections revealed 12 sequence types (STs) belonging to eight genetically distinct lineages. Only two novel STs were recovered (one isolate of each), indicating that isolates in this study were similar to those from previous studies of disease and carriage. However, ST59, the most common genotype recovered (from six individuals), may be adept at causing subcutaneous lesions in this patient population, as it is rare in carriage and disease. PCR detection of 22 toxin genes revealed a high prevalence of the gene for staphylococcal enterotoxin B compared with previous studies, indicating that this toxin may promote infections in this patient group.

Community-acquired Methicillin-resistant Staphylococcus aureus: Epidemiology and Potential Virulence Factors

Methicillin-resistant Staphylococcus aureus (MRSA) has been isolated from patients in the community. Some of these strains may have origins in the hospital, but others appear to be novel and unrelated to known hospital strains. Community MRSA strains have several distinguishing characteristics that may enable them to more readily colonize and infect otherwise healthy individuals. This article reviews recent publications addressing the epidemiology of MRSA in the community, risk factors associated with carriage, potentially associated virulence factors, and concepts of strain fitness as they pertain to MRSA. MRSA likely will be an increasingly important pathogen in the community.