Risk factors for transmission of carbapenem-resistant Enterobacterales to healthcare personnel gloves and gowns in the USA.

BACKGROUND: Hospitals are sources for acquisition of carbapenem-resistant Entero-bacterales (CRE), and it is believed that the contamination of healthcare personnel (HCP) hands and clothing play a major role in patient-to-patient transmission of antibiotic-resistant bacteria. AIM: The aim of this study was to determine which HCP types, HCP-patient interactions, and patient characteristics are associated with greater transmission of CRE to HCP gloves and gowns in the hospital. METHODS: This was a prospective observational cohort study that enrolled patients with recent surveillance or clinical cultures positive for CRE at five hospitals in four states in the USA. HCP gloves and gown were cultured after patient care. Samples were also obtained from patients' stool, perianal area, and skin of the chest and arm to assess bacterial burden. FINDINGS: Among 313 CRE-colonized patients and 3070 glove and gown cultures obtained after patient care, HCP gloves and gowns were found to be contaminated with CRE 7.9% and 4.3% of the time, respectively. Contamination of either gloves or gowns occurred in 10.0% of interactions. Contamination was highest (15.3%) among respiratory therapists (odds ratio: 3.79; 95% confidence interval: 1.61-8.94) and when any HCP touched the patient (1.52; 1.10-2.12). Associations were also found between CRE transmission to HCP gloves or gown and: being in the intensive care unit, having a positive clinical culture, and increasing bacterial burden on the patient. CONCLUSION: CRE transmission to HCP gloves and gown occurred frequently. These findings may inform evidence-based policies about what situations and for which patients contact precautions are most important.

Sociodemographic factors associated with patients hospitalised for coccidioidomycosis in California and Arizona, State Inpatient Database 2005-2011.

Coccidioidomycosis is endemic in the Southwestern United States. Disseminated infection can be life-threatening and is responsible for hospitalisation and significant healthcare resource utilisation. There are limited data evaluating factors associated with hospitalisation for coccidioidomycosis. We conducted a cross-sectional study to assess incidence and factors associated with coccidioidomycosis-associated hospitalisation in California and Arizona. We analysed hospital discharge data obtained from the State Inpatient Dataset for California and Arizona between 2005 and 2011 and performed multivariable logistic regression examining factors associated with coccidioidomycosis-associated hospitalisation. During our time frame, we found 23 758 coccidioidomycosis-associated hospitalisations. Coccidioidomycosis incidence was over sixfold higher in Arizona compared to California (198.9 vs. 29.6/100 000 person-years). In our multivariable model, coccidioidomycosis-associated hospitalisation was associated with age group 40-49 years (referent group: age 18-29 years, adjusted odds ratio (aOR) = 1.50 (95% confidence interval (CI) 1.43-1.59)), African American race (referent group: Caucasian, aOR = 1.98 (95% CI 1.89-2.06)), residing in a large rural town (referent group: urban area, aOR = 2.28 (95% CI 2.19-2.39)), uncomplicated diabetes (aOR = 1.47 (95% CI 1.41-1.52)) chronic obstructive pulmonary disease (aOR = 1.59 (95% CI 1.54-1.65)) and higher number of comorbidities (aOR = 1.02 (95% CI 1.02-1.03) for each point in the Elixhauser score). Identifying persons at highest risk for hospitalisation with coccidioidomycosis may be helpful for future prevention efforts.

Bayesian evidence and epidemiological implications of environmental contamination from acute respiratory infection in long-term care facilities.

Skilled nursing home facilities (SNFs) house a vulnerable population frequently exposed to respiratory pathogens. Our study aims to gain a better understanding of the transmission of nursing home-acquired viral respiratory infections in non-epidemic settings. Symptomatic surveillance was performed in three SNFs for residents exhibiting acute respiratory symptoms. Environmental surveillance of five high-touch areas was performed to assess possible transmission. All resident and environmental samples were screened using a commercial multiplex polymerase chain reaction platform. Bayesian methods were used to evaluate environmental contamination. Among nursing home residents with respiratory symptoms, 19% had a detectable viral pathogen (parainfluenza-3, rhinovirus/enterovirus, RSV, or influenza B). Environmental contamination was found in 20% of total room surface swabs of symptomatic residents. Environmental and resident results were all concordant. Target period prevalence among symptomatic residents ranged from 5.5 to 13.3% depending on target. Bayesian analysis quantifies the probability of environmental shedding due to parainfluenza-3 as 92.4% (95% CI: 86.8-95.8%) and due to rhinovirus/enterovirus as 65.6% (95% CI: 57.9-72.5%). Our findings confirm that non-epidemic viral infections are common among SNF residents exhibiting acute respiratory symptoms and that environmental contamination may facilitate further spread with considerable epidemiological implications. Findings further emphasise the importance of environmental infection control for viral respiratory pathogens in long-term care facilities.

Discontinuation of contact precautions with the introduction of universal daily chlorhexidine bathing.

Contact precautions are a traditional strategy to prevent transmission of methicillin-resistant Staphylococcus aureus (MRSA). Chlorhexidine bathing is increasingly used to decrease MRSA burden and transmission in intensive care units (ICUs). We sought to evaluate a hospital policy change from routine contact precautions for MRSA compared with universal chlorhexidine bathing, without contact precautions. We measured new MRSA acquisition in ICU patients and surveyed for MRSA environmental contamination in common areas and non-MRSA patient rooms before and after the policy change. During the baseline and chlorhexidine bathing periods, the number of patients (453 vs. 417), ICU days (1999 vs. 1703) and MRSA days/1000 ICU days (109 vs. 102) were similar. MRSA acquisition (2/453 vs. 2/457, P = 0·93) and environmental MRSA contamination (9/474 vs. 7/500, P = 0·53) were not significantly different between time periods. There were 58% fewer contact precaution days in the ICU during the chlorhexidine period (241/1993 vs. 102/1730, P < 0·01). We found no evidence that discontinuation of contact precautions for patients with MRSA in conjunction with adoption of daily chlorhexidine bathing in ICUs is associated with increased MRSA acquisition among ICU patients or increased MRSA contamination of ICU fomites. Although underpowered, our findings suggest this strategy, which has the potential to reduce costs and improve patient safety, should be assessed in similar but larger studies.

Incidence and factors associated with emergency department visits for recurrent skin and soft tissue infections in patients in California, 2005-2011.

More than 2 million visits for skin and soft tissue infections (SSTIs) are seen in US emergency departments (EDs) yearly. Up to 50% of patients with SSTIs, suffer from recurrences, but associated factors remain poorly understood. We performed a retrospective study of patients with primary diagnosis of SSTI between 2005 and 2011 using California ED discharge data from the State Emergency Department Databases and State Inpatient Databases. Using a multivariable logistic regression, we examined factors associated with a repeat SSTI ED visits up to 6 months after the initial SSTI. Among 197 371 SSTIs, 16·3% were associated with a recurrent ED visit. We found no trend in recurrent visits over time (χ 2 trend = 0·68, P = 0·4). Race/ethnicity, age, geographical location, household income, and comorbidities were all associated with recurrent visits. Recurrent ED visits were associated with drug/alcohol abuse or liver disease [odds ratio (OR) 1·4, 95% confidence interval (CI) 1·3-1·4], obesity (OR 1·3, 95% CI 1·2-1·4), and in infections that were drained (OR 1·1, 95% CI 1·1-1·1) and inversely associated with hospitalization after initial ED visit (OR 0·4, 95% CI 0·3-0·4). In conclusion, we found several patient-level factors associated with recurrent ED visits. Identification of these high-risk groups is critical for future ED-based interventions.

Potential economic burden of carbapenem-resistant Enterobacteriaceae (CRE) in the United States.

OBJECTIVES: The Centers for Disease Control and Prevention considers carbapenem-resistant Enterobacteriaceae (CRE) an urgent public health threat; however, its economic burden is unknown. METHODS: We developed a CRE clinical and economics outcomes model to determine the cost of CRE infection from the hospital, third-party payer, and societal, perspectives and to evaluate the health and economic burden of CRE to the USA. RESULTS: Depending on the infection type, the median cost of a single CRE infection can range from $22 484 to $66 031 for hospitals, $10 440 to $31 621 for third-party payers, and $37 778 to $83 512 for society. An infection incidence of 2.93 per 100 000 population in the USA (9418 infections) would cost hospitals $275 million (95% CR $217-334 million), third-party payers $147 million (95% CR $129-172 million), and society $553 million (95% CR $303-1593 million) with a 25% attributable mortality, and would result in the loss of 8841 (95% CR 5805-12 420) quality-adjusted life years. An incidence of 15 per 100 000 (48 213 infections) would cost hospitals $1.4 billion (95% CR $1.1-1.7 billion), third-party payers $0.8 billion (95% CR $0.6-0.8 billion), and society $2.8 billion (95% CR $1.6-8.2 billion), and result in the loss of 45 261 quality-adjusted life years. CONCLUSIONS: The cost of CRE is higher than the annual cost of many chronic diseases and of many acute diseases. Costs rise proportionally with the incidence of CRE, increasing by 2.0 times, 3.4 times, and 5.1 times for incidence rates of 6, 10, and 15 per 100 000 persons.

Patient-level analysis of incident vancomycin-resistant enterococci colonization and antibiotic days of therapy.

Vancomycin-resistant enterococci (VRE) infections are a public health threat associated with increased patient mortality and healthcare costs. Antibiotic usage, particularly cephalosporins, has been associated with VRE colonization and VRE bloodstream infections (VRE BSI). We examined the relationship between antimicrobial usage and incident VRE colonization at the individual patient level. Prospective, weekly surveillance was undertaken for incident VRE colonization defined by negative admission but positive surveillance swab in a medical intensive care unit over a 17-month period. Antimicrobial exposure was quantified as days of therapy (DOT)/1000 patient-days. Multiple logistic regression was used to analyse incident VRE colonization and antibiotic DOT, controlling for demographic and clinical covariates. Ninety-six percent (1398/1454) of admissions were swabbed within 24 h of intensive care unit (ICU) arrival and of the 380 patients in the ICU long enough for weekly surveillance, 83 (22%) developed incident VRE colonization. Incident colonization was associated in bivariate analysis with male gender, more previous hospital admissions, longer previous hospital stay, and use of cefepime/ceftazidime, fluconazole, azithromycin, and metronidazole (P < 0·05). After controlling for demographic and clinical covariates, metronidazole was the only antibiotic independently associated with incident VRE colonization (odds ratio 2·0, 95% confidence interval 1·2-3·3, P < 0·009). Our findings suggest that risk of incident VRE colonization differs between individual antibiotic agents and support the possibility that antimicrobial stewardship may impact VRE colonization and infection.

The economic burden of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA).

The economic impact of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) remains unclear. We developed an economic simulation model to quantify the costs associated with CA-MRSA infection from the societal and third-party payer perspectives. A single CA-MRSA case costs third-party payers $2277-$3200 and society $7070-$20 489, depending on patient age. In the United States (US), CA-MRSA imposes an annual burden of $478 million to 2.2 billion on third-party payers and $1.4-13.8 billion on society, depending on the CA-MRSA definitions and incidences. The US jail system and Army may be experiencing annual total costs of $7-11 million ($6-10 million direct medical costs) and $15-36 million ($14-32 million direct costs), respectively. Hospitalization rates and mortality are important cost drivers. CA-MRSA confers a substantial economic burden on third-party payers and society, with CA-MRSA-attributable productivity losses being major contributors to the total societal economic burden. Although decreasing transmission and infection incidence would decrease costs, even if transmission were to continue at present levels, early identification and appropriate treatment of CA-MRSA infections before they progress could save considerable costs.

A comparison of clinical outcomes between healthcare-associated infections due to community-associated methicillin-resistant Staphylococcus aureus strains and healthcare-associated methicillin-resistant S. aureus strains.

There are limited data examining whether outcomes of methicillin-resistant Staphylococcus aureus (MRSA) healthcare-associated infections (HAIs) are worse when caused by community-associated (CA) strains compared to HA strains. We reviewed all patients' charts at our institution from 1999 to 2009 that had MRSA first isolated only after 72 h of hospitalization (n=724). Of these, 384 patients had a MRSA-HAI according to CDC criteria. Treatment failure was similar in those infected with a phenotypically CA-MRSA strain compared to a phenotypically HA-MRSA strain (23% vs. 15%, P=0.10) as was 30-day mortality (16% vs. 19%, P=0.57). Independent risk factors associated with (P<0.05) treatment failure were higher Charlson Comorbidity Index, higher APACHE II score, and no anti-MRSA treatment. These factors were also associated with 30-day mortality, as were female gender, older age, MRSA bloodstream infection, MRSA pneumonia, and HIV. Our findings suggest that clinical and host factors, not MRSA strain type, predict treatment failure and death in hospitalized patients with MRSA-HAIs.

Pneumocystis pneumonia in hospitalized patients: a detailed examination of symptoms, management, and outcomes in human immunodeficiency virus (HIV)-infected and HIV-uninfected persons.

BACKGROUND: Pneumocystis jirovecii pneumonia (PCP) is a life-threatening infection for immunocompromised individuals. Robust data and clear guidelines are available for prophylaxis and treatment of human immunodeficiency virus (HIV)-related PCP (HIV-PCP), yet few data and no guidelines are available for non-HIV-related PCP (NH-PCP). We postulated that prevention and inpatient management of HIV-PCP differed from NH-PCP. METHODS: We performed a retrospective case review of all pathologically confirmed cases of PCP seen at the University of Alabama Medical Center from 1996 to 2008. Data on clinical presentation, hospital course, and outcome were collected using a standardized data collection instrument. Bivariate analysis compared prophylaxis, adjunctive corticosteroids, and clinical outcomes between patients with HIV-PCP and NH-PCP. RESULTS: Our analysis of the cohort included 97 cases of PCP; 65 HIV and 32 non-HIV cases. Non-HIV cases rarely received primary prophylaxis (4% vs. 38%, P = 0.01) and received appropriate antibiotics later in the course of hospitalization (5.2 days vs. 1.1 days, P < 0.005). Among transplant patients, NH-PCP was diagnosed a mean of 1066 days after transplantation and most patients were on low-dose corticosteroids (87%) at the time of disease onset. No significant differences in adjunctive corticosteroid use (69% vs. 77%, P = 0.39) and 90-day mortality (41% vs. 28%, P = 0.20) were detected. CONCLUSIONS: Patients who have undergone organ or stem cell transplant remain at risk for PCP for many years after transplantation. In our cohort, patients who developed NH-PCP were rarely given prophylaxis, and initiation of appropriate antibiotics was significantly delayed compared to cases of HIV-PCP. Medical providers should be aware of the ongoing risk for NH-PCP, even late after transplantation, and consider more aggressive approaches to both prophylaxis and earlier empirical therapy for PCP.

Non-suppurative cellulitis: risk factors and its association with Staphylococcus aureus colonization in an area of endemic community-associated methicillin-resistant S. aureus infections.

Suppurative methicillin-resistant Staphylococcus aureus (MRSA) skin infections are common and associated with MRSA colonization, but little is known about non-suppurative cellulitis and its relationship with MRSA colonization in areas endemic for community-associated MRSA. We prospectively enrolled patients hospitalized for non-suppurative cellulitis (n=50) and matched controls (n=100) and found S. aureus colonization was similar in cases and controls (30% vs. 25%, P=0·95). MRSA was uncommon in cases (6%) and controls (3%) (P=0·39). All MRSA isolates were USA300 by pulsed-field gel electrophoresis. Independent risk factors for non-suppurative cellulitis were diabetes (OR 3·5, 95% CI 1·4-8·9, P=0·01) and homelessness in the previous year (OR 6·4, 95% CI 1·9-20·9, P=0·002). These findings suggest that MRSA may only rarely be causative of non-suppurative cellulitis.

Patients with methicillin-resistant Staphylococcus aureus infection: twenty-first century lepers.

In the recent past, there has been a rapid increase in the incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections, especially community-associated (CA)-MRSA. Many media descriptions of MRSA are sensational and focus on its potential for severe disease and contagiousness. Our objective is to describe psychological and social morbidity associated with MRSA infection via a case series of five patients with CA-MRSA infection. We also analyse the resulting stigmatization associated with being diagnosed with MRSA infection. We learned that patients describe a variety of stigmatization related to their diagnosis of MRSA, including being shunned at home and in the workplace. Patients describe being asked by family, colleagues, and clients to take extraordinary measures to prevent MRSA transmission. Consequences of MRSA diagnoses have included erosion or termination of key personal and business relationships. In conclusion, stigmatization resulting from the diagnosis of MRSA can have profound personal and social morbidity. Media and public health awareness of MRSA infection needs to be balanced with information about how MRSA transmission is usually preventable with simple hygienic measures.

Staphylococcus aureus is the most common identified cause of cellulitis: a systematic review.

We utilized Medline to perform a systematic review of the literature to quantify the aetiology of cellulitis with intact skin. Of 808 patients with cellulitis, 127-129 (15.7-16.0%) patients had positive needle aspiration and/or punch biopsy cultures from intact skin. Of the patients with positive cultures, 65 (50.4-51.2%) had cultures positive for Staphylococcus aureus, 35 (27.1-27.6%) for group A streptococcus, and 35-37 (27.1-29.1%) for other pathogens. The most common aetiology of cellulitis with intact skin, when it can be determined, is S. aureus, outnumbering group A streptococcus by a ratio of nearly 2:1. Given the increasing incidence of community-associated methicillin-resistant S. aureus infections, our findings may have critical therapeutic implications.

Body site colonization in patients with community-associated methicillin-resistant Staphylococcus aureus and other types of S. aureus skin infections.

Efforts to control spread of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are often based on eradication of colonization. However, the role of nasal and non-nasal colonization in the pathogenesis of these infections remains poorly understood. Patients with acute S. aureus skin and soft tissue infection (SSTI) were prospectively enrolled. Each subject's nasal, axillary, inguinal and rectal areas were swabbed for S. aureus and epidemiological risk factors were surveyed. Among the 117 patients enrolled, there were 99 patients who had an SSTI and for whom data could be analysed. Sixty-five patients had a CA-MRSA SSTI. Among these patients, MRSA colonization in the nares, axilla, inguinal area and rectum was 25, 6, 11 and 13%, respectively, and 37% overall were MRSA colonized. Most (96%) MRSA colonization was detected using nose and inguinal screening alone. Non-nasal colonization was 25% among CA-MRSA patients, but only 6% among patients with CA-methicillin-susceptible S. aureus (MSSA) or healthcare-associated MRSA or MSSA. These findings suggest that colonization patterns in CA-MRSA infection are distinct from those in non-CA-MRSA S. aureus infections. The relatively high prevalence of non-nasal colonization may play a key role in CA-MRSA transmission and acquisition of infection.

Arsenic(III) fuels anoxygenic photosynthesis in hot spring biofilms from Mono Lake, California.

Phylogenetic analysis indicates that microbial arsenic metabolism is ancient and probably extends back to the primordial Earth. In microbial biofilms growing on the rock surfaces of anoxic brine pools fed by hot springs containing arsenite and sulfide at high concentrations, we discovered light-dependent oxidation of arsenite [As(III)] to arsenate [As(V)] occurring under anoxic conditions. The communities were composed primarily of Ectothiorhodospira-like purple bacteria or Oscillatoria-like cyanobacteria. A pure culture of a photosynthetic bacterium grew as a photoautotroph when As(III) was used as the sole photosynthetic electron donor. The strain contained genes encoding a putative As(V) reductase but no detectable homologs of the As(III) oxidase genes of aerobic chemolithotrophs, suggesting a reverse functionality for the reductase. Production of As(V) by anoxygenic photosynthesis probably opened niches for primordial Earth's first As(V)-respiring prokaryotes.

Societal costs versus savings from wild-card patent extension legislation to spur critically needed antibiotic development.

BACKGROUND: Over the last two decades, an alarming rise in infections caused by antibiotic-resistant microbes has been paralleled by an equally alarming decline in the development of new antibiotics to deal with the threat. In response to this brewing "perfect storm" of infectious diseases, the Infectious Diseases Society of America (IDSA) has released a white paper that proposes incentives to stimulate critically needed antibiotic development by pharmaceutical companies. A cornerstone of the recommendations is establishment of a "wild-card patent extension" program. This program would allow a company receiving United States (US) Food and Drug Administration (FDA) approval for a new anti-infective agent targeting a drug-resistant pathogen to extend the patent on a drug within their active portfolio. However, wild-card patent extension legislation is highly controversial due to concerns regarding its societal cost. METHODS: We performed a systematic literature review to estimate the societal cost of wild-card patent extension compared to the savings resulting from the availability of one new antibiotic to treat multi-drug-resistant Pseudomonas aeruginosa. RESULTS: We conservatively estimate that wild-card patent extension applied to one new antibiotic would cost $7.7 billion over the first 2 years, and $3.9 billion over the next 18 years. Thus, even if the new antibiotic abrogated only 50% of the annual societal cost of multidrug-resistant P. aeruginosa (estimated $2.7 billion), wild-card patent extension would be cost neutral by 10 years after approval of the new antibiotic, and would save society approximately $4.6 billion by 20 years after approval. CONCLUSIONS: Wild-card patent extension appears to be a cost-effective strategy to spur anti-infective development. Although our analysis is limited by the precision of published data, our model employed conservative assumptions.

Dissimilatory arsenate and sulfate reduction in sediments of two hypersaline, arsenic-rich soda lakes: Mono and Searles Lakes, California.

A radioisotope method was devised to study bacterial respiratory reduction of arsenate in sediments. The following two arsenic-rich soda lakes in California were chosen for comparison on the basis of their different salinities: Mono Lake (approximately 90 g/liter) and Searles Lake (approximately 340 g/liter). Profiles of arsenate reduction and sulfate reduction were constructed for both lakes. Reduction of [73As]arsenate occurred at all depth intervals in the cores from Mono Lake (rate constant [k] = 0.103 to 0.04 h(-1)) and Searles Lake (k = 0.012 to 0.002 h(-1)), and the highest activities occurred in the top sections of each core. In contrast, [35S]sulfate reduction was measurable in Mono Lake (k = 7.6 x10(4) to 3.2 x 10(-6) h(-1)) but not in Searles Lake. Sediment DNA was extracted, PCR amplified, and separated by denaturing gradient gel electrophoresis (DGGE) to obtain phylogenetic markers (i.e., 16S rRNA genes) and a partial functional gene for dissimilatory arsenate reduction (arrA). The amplified arrA gene product showed a similar trend in both lakes; the signal was strongest in surface sediments and decreased to undetectable levels deeper in the sediments. More arrA gene signal was observed in Mono Lake and was detectable at a greater depth, despite the higher arsenate reduction activity observed in Searles Lake. A partial sequence (about 900 bp) was obtained for a clone (SLAS-3) that matched the dominant DGGE band found in deeper parts of the Searles Lake sample (below 3 cm), and this clone was found to be closely related to SLAS-1, a novel extremophilic arsenate respirer previously cultivated from Searles Lake.

Empirical therapy for uncomplicated urinary tract infections in an era of increasing antimicrobial resistance: a decision and cost analysis.

Infectious Diseases Society of America guidelines state that uncomplicated urinary tract infections (UTIs) should be treated empirically with trimethoprim-sulfamethoxazole (TMP-SMZ), unless the community resistance among uropathogens exceeds 10%-20%, in which case a fluoroquinolone (FQ) should be used. However, the data to support this threshold are limited. We performed a cost-minimization and sensitivity analysis to determine what level of TMP-SMZ resistance in a community should trigger FQ use. The mean cost of empirical treatment with TMP-SMZ was US$92 when the proportion of resistant Escherichia coli was 0%, $106 when it was 20%, and $120 when it was 40%. The mean cost of empirical FQ treatment was $107 at current levels of FQ resistance. When >22% of E. coli in a community are TMP-SMZ-resistant, empirical FQ therapy becomes less costly than TMP-SMZ therapy. Treatment guidelines for empirical treatment of UTIs may need modification, and the threshold trigger for empirical FQ use should be raised to >20% TMP-SMZ resistance.

A comparison study of multiple measures of adherence to HIV protease inhibitors.

BACKGROUND: Poor adherence to HIV protease inhibitors may compromise the effectiveness of treatment. Few studies have compared methods for measuring adherence or have related adherence measures to a clinical outcome. OBJECTIVE: To examine the relationship among a composite score of adherence, the three primary measures of adherence, and HIV virologic response. DESIGN: Longitudinal cohort study. SETTING: Public HIV clinic. PATIENTS: 108 HIV-infected adults receiving protease inhibitors or non-nucleoside reverse transcriptase inhibitors who were monitored for 666 monthly intervals. MEASUREMENTS: Medication Event Monitoring System (MEMS), pill count, and interview combined into a composite adherence score (CAS), and HIV viral load. RESULTS: Mean antiretroviral adherence differed by adherence measure (MEMS, 0.63; pill count, 0.83; interview, 0.93; and CAS, 0.76). Composite adherence score decreased significantly over time. Composite adherence score, MEMS values, pill values, and interview values were statistically significantly associated with achievement of an undetectable viral load within 6 months of initiating therapy. Composite adherence score showed the strongest predictive relationship (odds ratios for a 10% increase in adherence for CAS, MEMS, pill count, and interview, respectively, were 1.26 [95% CI, 1.16 to 1.37], 1.13 [CI, 1.06 to 1.21], 1.10 [CI, 1.02 to 1.19], and 1.35 [CI, 0.94 to 1.94]). CONCLUSIONS: Different measures applied to the same patient suggest different levels of adherence. Adherence may be underestimated by MEMS and overestimated by pill count and interview. A summary measure combining several measures is more strongly related to a clinical response, but more practical measurement methods are needed for clinical use.