COVID-19 Vaccination Uptake, Infection Rates, and Seropositivity Among Youth Experiencing Homelessness in the United States.

BACKGROUND: People experiencing homelessness are at greater risk of exposure and poor health outcomes from COVID-19. Yet, little data exists on the prevalence and correlates of COVID-19 among homeless populations. To mitigate the spread and severity, uptake of the COVID-19 vaccine is needed. This can be challenging among youth experiencing homelessness who are more likely to be unvaccinated when compared to stably housed youth. OBJECTIVE: We conducted this study to determine the prevalence and correlates of COVID-19 among youth experiencing homelessness. METHODS: We examined experiences of COVID-19 symptoms, self-report of infection, rates of COVID-19 antibodies and distinguished between natural and vaccinated immunity among youth experiencing homelessness (N = 265) recruited in one large metropolitan area in the South. RESULTS: Based on self-report, very few participants experienced any symptoms, and 80% had never been diagnosed with COVID-19. Of those with COVID-19 antibodies (68%), the proportion with antibodies resulting from natural infection was 44%. The vaccination rate was 42%. Younger and vaccinated participants and those in shelters were likelier to have COVID-19 antibodies. Black and Hispanic youth were more likely than White youth to have had COVID-19. Those who adopted only one or two prevention behaviors were more likely to acquire a natural infection than those who adopted three or more prevention behaviors. DISCUSSION: Youth experiencing homelessness report low vaccination rates, disrupted access to health care and social supports, and underlying chronic conditions, which may explain why they face poorer outcomes when infected with COVID-19. Vaccination and risk mitigation strategies to combat the high prevalence of COVID-19 are especially needed for sheltered youth who are at high risk yet are often asymptomatic.

Guidelines for resident training in veterinary clinical pathology. IV: Laboratory quality management-Teaching domains, competencies, and suggested learning outcomes.

BACKGROUND: The 2019 ASVCP Education Committee Forum for Discussion, presented at the annual ASVCP/ACVP meeting, identified a need to develop recommendations for teaching laboratory quality management principles in veterinary clinical pathology residency training programs. OBJECTIVES: To present a competency-based framework for teaching laboratory quality management principles in veterinary clinical pathology residency training programs, including entrustable professional activities (EPAs), domains of competence, individual competencies, and learning outcomes. METHODS: A joint subcommittee of the ASVCP Quality Assurance and Laboratory Standards (QALS) and Education Committees executed this project. A draft guideline version was reviewed by the ASVCP membership and shared with selected ACVP committees in early 2022, and a final version was voted upon by the full QALS and Education Committees in late 2022. RESULTS: Eleven domains of competence with relevant individual competencies were identified. In addition, suggested learning outcomes and resource lists were developed. Domains and individual competencies were mapped to six EPAs. CONCLUSIONS: This guideline presents a framework for teaching principles of laboratory quality management in veterinary clinical pathology residency training programs and was designed to be comprehensive yet practical. Guidance on pedagogical terms and possible routes of implementation are included. Recommendations herein aim to improve and support resident training but may require gradual implementation, as programs phase in necessary expertise and resources. Future directions include the development of learning milestones and assessments and consideration of how recommendations intersect with the American College of Veterinary Pathologists training program accreditation and certifying examination.

Invasive Mold Infections Following Hurricane Harvey-Houston, Texas.

Background: Characterizing invasive mold infection (IMI) epidemiology in the context of large flooding events is important for public health planning and clinical decision making. Methods: We assessed IMI incidence (per 10 000 healthcare encounters) 1 year before and after Hurricane Harvey at 4 hospitals in Houston, Texas. Potential IMI cases were assigned as proven or probable cases using established definitions, and surveillance cases using a novel definition. We used rate ratios to describe IMI incidence and multivariable logistic regression to examine patient characteristics associated with IMI case status. Results: IMI incidence was significantly higher posthurricane (3.69 cases) than prehurricane (2.50 cases) (rate ratio, 1.48 [95% confidence interval, 1.10-2.00]), largely driven by surveillance IMI cases. Aspergillus was the most common species cultured (33.5% prehurricane and 39.9% posthurricane). About one-quarter (25.8%) of IMI patients lacked classical IMI risk factors such as hematologic malignancy and transplantations. Overall, 45.1% of IMI patients received intensive care, and in-hospital all-cause mortality was 24.2%. Conclusions: IMI incidence likely increased following Hurricane Harvey and outcomes for IMI patients were severe. Patient and clinician education on IMI prevention and identification is warranted, particularly as the frequency of extreme weather events increases due to climate change.

Airway remodeling in horses with mild and moderate asthma.

BACKGROUND: There is a remodeling of the central airways in horses with severe asthma but whether a similar process occurs in horses with the mild or moderate asthma (MMA) is unknown. OBJECTIVES: To evaluate lesions affecting the central airways of horses with MMA. ANIMALS: Twelve horses with MMA and 8 control horses. METHODS: Case-control retrospective study of horses classified as MMA affected or controls based on history and bronchoalveolar lavage fluid cytology. Endobronchial biopsies were analyzed using histomorphometry and a semiquantitative histologic scoring system. RESULTS: Histomorphometry identified epithelial hyperplasia (47 µm2 /µm [34-57 µm2 /µm]; P = .02), a thickened lamina propria (166 µm [73-336 µm]; P = .04), and smooth muscle fibrosis (42% [33%-78%]; P = .04) in horses with MMA when compared to controls horses (24 µm2 /µm [21-80 µm2 /µm]; 76 µm [36-176 µm]; and 33% [26%-52%], respectively). The semiquantitative score results indicated, in horses with MMA, the presence of epithelial hyperplasia (7 of the 12 horses with MMA and only 1 of the 8 control horses had a score of 1/1), and submucosal inflammatory leucocytes in the central airway (11 of the 12 horses with MMA and only 4 of the 8 control horses had a score ≥ 1/2). CONCLUSIONS AND CLINICAL RELEVANCE: Tissue remodeling of the bronchial lamina propria, epithelium, and smooth muscle was present in horses with MMA.

Retrospective investigation of automated hematology analyzer-determined indicators of neutrophil activation in blood samples from horses with asthma.

OBJECTIVE: To investigate indicators of neutrophil activation in the blood of healthy and asthma-affected horses and assess associations between corticosteroid treatment and these variables. ANIMALS: 48 horses (14 with severe equine asthma [SEA], 21 with mild to moderate equine asthma [MEA], and 13 healthy controls). PROCEDURES: In a 3-part retrospective study, hematology analyzer data for horses included in previous studies were reviewed. Neutrophil size, neutrophil light absorbance (NLA), and myeloperoxidase (MPO) index were recorded. Data for each variable were compared among groups for the entire study sample (part 1). Changes in each variable were assessed for one subset of horses (5 SEA-affected and 6 controls) after treatment for 2 weeks with dexamethasone (0.06 mg/kg, PO, q 24 h; part 2) and for another subset (8 SEA-affected horses) after the same treatment and after a 1-week posttreatment washout period (part 3). RESULTS: All 3 variables were significantly greater for the SEA group, compared with the MEA and control groups in part 1. Following dexamethasone treatment, the control- and SEA-group NLA and MPO index significantly decreased and SEA-group neutrophil size significantly decreased in part 2; immediate posttreatment results for SEA-affected horses were similar in part 3, with significantly increased neutrophil size and nonsignificant increases in NLA and MPO index following washout. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested horses with exacerbated SEA have larger neutrophils that contain more MPO, compared with neutrophils of MEA-affected and healthy control horses. The clinical value of these variables for the diagnosis of equine asthma was deemed limited owing to data overlap among groups.

Effects of different drying methods on smears of canine blood and effusion fluid.

BACKGROUND: Glass slide preparations from a variety of specimens (blood, masses, effusions) are commonly made as part of the diagnostic work-up, however the effects of various drying methods in veterinary practice and diagnostic laboratory settings is not clear. OBJECTIVE: Compare the effects of four drying methods on results of microscopic examination of canine blood smears and direct smears of pleural or peritoneal effusion fluid. METHODS: Twelve canine blood samples (6 from healthy dogs, 6 from sick dogs) and 6 canine peritoneal or pleural effusion samples. Four smears were prepared from each of the 18 samples and dried using the following methods: air-dry, hair dryer with or without heat, and heat block at 58 °C. Observers, blinded to the drying method, independently reviewed the slides microscopically, using a scoring system to evaluate cell morphology and (for blood smears) echinocyte numbers; scoring results were analyzed statistically. RESULTS: For blood smears, several comparisons showed more adverse effects on morphology using the heat block method than for one or more other drying methods. For effusion fluid smears, RBCs dried with the heat block or air-dry methods had more poorly preserved morphology than RBCs dried by the hair dryer method without heat. CONCLUSIONS AND CLINICAL RELEVANCE: The results (1) indicate that different drying methods had a significant effect, (2) support using a hair dryer without heat for both blood smears and effusion fluid smears, and (3) discourage using a 58 °C heat block.

Evaluation of 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6'-methylresorufin) ester lipase concentrations in cats with kidney disease and with normal SNAP fPL.

Measuring 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6'-methylresorufin) ester (DGGR) lipase activity is a cost-effective test for diagnosing pancreatitis compared to the feline pancreas-specific lipase (Spec fPL) test. However, little is known about the influence of renal insufficiency on DGGR lipase in cats. This study evaluated the influence of renal function on serum DGGR lipase in the cat. Serum samples from 49 cats with normal pancreas-specific lipase immunoreactivity were analyzed for DGGR lipase activity and serum creatinine. Median serum DGGR lipase activity for cats with kidney disease (KD+) was 22 IU/L (range: 9 to 29 IU/L), whereas for cats without kidney disease (KD-) and healthy cats, the medians were 16 IU/L (range: 6 to 32 IUI/L), and 15 IU/L (range: 9 to 23 IU/L), respectively. The KD+ group had significantly higher DGGR lipase concentrations compared to the healthy group (P = 0.030), but most results were within the reference range. There was a weak positive correlation between creatinine and DGGR lipase values (R 2 = 19.6%; P = 0.0014) and no significant correlation between symmetric dimethylarginine (SDMA) and DGGR lipase. Key clinical message: Although cats with kidney disease had significantly higher serum DGGR lipase concentrations than the healthy controls, the difference was small and does not appear to be clinically relevant.

Évaluation de la concentration de la lipase de l'ester de l'1,2-o-dilauryl-rac-glycero-3-acide glutarique-(6'-methylresorufine) chez les chats présentant une maladie rénale et un SNAP fPL normal. La lipase d'ester 1,2-o-dilauryl-rac-glycero-3-glutarique ester (6'-méthylrésorufine) (DGGR) semble être utile pour le diagnostic ante-mortem de pancréatite et s'avère également une méthode économique par rapport au dosage de la lipase féline spécifique du pancréas (Spec fPL). Toutefois, l'influence de l'insuffisance rénale sur la lipase DGGR, est encore méconnue chez le chat. Le but de cette étude prospective est d'établir l'influence de la fonction rénale sur la lipase DGGR chez les chats. Du sérum a été prélevé chez 49 chats ayant un test semi-quantitatif normal pour l'estimation de l'immunoréactivité pancréatique féline (SNAP fPL) et a été analysé pour déterminer l'activité sérique de la DGGR lipase et de la créatinine. La médiane sérique de la lipase DGGR chez les chats atteints de maladie rénale (groupe KD+) était de 22 (intervalle: 9­29) UI/L, tandis que celle des chats sans maladie rénale (groupe KD−) et celle des chats sains était de 16 (6­32) UI/L et 15 (9­23) UI/L, respectivement. Le groupe KD+ présentait des concentrations sériques de lipase DGGR significativement plus élevées que le groupe de chats sains (P = 0,030), mais la plupart des résultats se situaient dans les valeurs de référence. Il y avait une corrélation positive statistiquement significative, mais faible, entre les valeurs de la créatinine et de la lipase de DGGR (R 2 = 19,6 %; P = 0,0014). Il n'y avait pas de corrélation significative entre la symétrique diméthylarginine (SDMA) et la lipase DGGR.Message clinique clé:Ainsi, les chats atteints d'une maladie rénale présentent des concentrations sériques de lipase DGGR significativement plus élevées que celles des chats sains. Cependant, la différence est légère et ne semble pas être cliniquement pertinente.(Traduit par les auteurs).

Cryptococcus gattii pneumonia in an adult horse which had travelled in an endemic area.

A gelding from eastern Canada was presented for cough and exercise intolerance 14 months after it had travelled on Vancouver Island. Cryptococcus gattii pneumonia was diagnosed based on cytology, antigen titers, and polymerase chain reaction (PCR). The horse was treated with fluconazole for 10 months. Delayed C. gattii infection can occur after travel in an endemic area.

Pneumonie à Cryptococcus gattii chez un cheval adulte ayant voyagé dans une région endémique. Un cheval hongre de l'est canadien fut présenté pour de la toux et de l'intolérance à l'exercice 14 mois après avoir voyagé sur l'Île de Vancouver. Une pneumonie à Cryptococcus gattii fut diagnostiquée sur la base de la cytologie, des titres antigéniques, et de la réaction d'amplification en chaîne par la polymérase (PCR). Le cheval fut traité avec du fluconazole pendant 10 mois. Une infection à retardement par C. gattii peut survenir à la suite d'un voyage dans une région endémique.(Traduit par Dr Serge Messier).

Effect of time and storage on toxic or pseudo-toxic change in canine neutrophils.

BACKGROUND: The presence of toxic change in neutrophils is frequently used as a biomarker of inflammation in dogs. OBJECTIVE: We aimed to evaluate the effect of time and storage on toxic change in canine neutrophils. METHODS: One hundred and fifty microliters of EDTA blood were obtained from eight dogs with no toxic neutrophil changes observed on fresh blood smears (T0). Blood was stored at room temperature (RT), in a box with an icepack (ICE), and at 4°C. For each storage condition, smears were prepared 2 (T2), 4 (T4), 8 (T8), and 24 (T24) hours post blood draw. Smears were randomized, and each smear was evaluated for the presence of toxic neutrophil change. RESULTS: A statistically significant effect of time and storage on the presence of toxic neutrophil change was observed. Compared with T0, the number of neutrophils containing Döhle bodies was significantly higher at T8 and T24 for the RT (P < 0.0001) and ICE (P < 0.0001) samples and at T24 for 4°C samples (P < 0.0001). Additionally, smears were falsely classified as having 1+ toxic change in 0/8 (T2), 1/8 (T4), 3/8 (T8), and 8/8 (T24) for RT samples; 0/8 (T2 and T4), 2/8 (T8), and 5/7 (T24) smears for ICE samples; and 0/8 (T2, T4, and T8) and 2/8 (T24) for 4°C samples. CONCLUSIONS: Smears can be falsely classified as having neutrophils with toxic change as early as 4 hours post blood draw in samples stored at RT, 8 hours when stored with icepacks, and 24 hours when stored at 4°C. Canine blood smears should be prepared and evaluated for toxic neutrophil change as early as possible.

Investigation of blood biomarkers for the diagnosis of mild to moderate asthma in horses.

BACKGROUND: Asthma in horses is associated with nonspecific respiratory clinical signs and may be manifested only as exercise intolerance. Its diagnosis relies on bronchoalveolar lavage fluid (BALF) cytology in the presence of compatible clinical signs. The identification of blood biomarkers for this condition would facilitate diagnosis in the field, because there are regional areas where BAL is not routinely performed in clinical practice. OBJECTIVE: Identification of blood biomarkers for the diagnosis of asthma in horses. ANIMALS: Fourteen horses with asthma with increased neutrophil numbers in BALF (neutrophilic asthma), 9 healthy control horses, and 10 horses with other pathologic conditions (pathologic controls). METHODS: Physical examination, clinical score, hematology, and BALF cytology (in a subset of horses) were performed. Serum concentrations of surfactant protein D (SP-D), haptoglobin, and secretoglobin (SCGB) were measured using commercial ELISA assays. RESULTS: Serum concentration of SP-D > 43 ng/mL, serum concentration of haptoglobin >5730 ng/mL, and serum concentration of SCGB <19 ng/mL allowed differentiation of horses with neutrophilic asthma from horses of the control groups (healthy and pathologic) with sensitivity of 55, 95, and 75%, and specificity of 67, 28, and 60%, respectively. Specificity of 100% and sensitivity of 45% were obtained with the combination of SP-D, haptoglobin, and SCGB at the serum concentrations indicated above. Specificity of 95% and sensitivity of 45% were obtained with the combination of SP-D and SCGB serum concentrations. CONCLUSIONS AND CLINICAL IMPORTANCE: Haptoglobin, SCGB, and SP-D may be diagnostic aids in horses with clinical signs of lower airway disease and neutrophilic pulmonary inflammation.

Polymerase chain reaction for antigen receptor rearrangement: Benchmarking performance of a lymphoid clonality assay in diverse canine sample types.

BACKGROUND: Polymerase chain reaction for antigen receptor rearrangement (PARR) is a molecular diagnostic tool used for discrimination of lymphoid malignancies in dogs from benign processes. Assay variations have been described and are commercially available, but performance metrics are not uniformly reported. OBJECTIVES: To describe performance (accuracy, sensitivity, specificity) and rigorous benchmarking of a PARR protocol (ePARR) in clinically relevant samples. ANIMALS: One hundred eighty-one client-owned dogs. METHODS: Lymphoma and benign tissues representative of the clinical spectrum with gold standard histopathologic and immunohistochemical diagnoses were collected. Assay development and benchmarking were performed on fresh frozen (FF) tissue, formalin-fixed paraffin-embedded (FFPE) tissue, flow cytometry pellets, and air-dried fine-needle aspirates (FNA). Assay performance was determined for FFPE from 56 dogs (18 B-cell lymphoma, 24 T-cell lymphoma, and 14 non-lymphoma), 80 frozen flow cytometry pellets (66 B-cell lymphoma, 14 T-cell lymphoma, 0 non-lymphoma), and 41 air-dried FNA slides (23 lymphoma, 18 non-lymphoma). RESULTS: For discrimination of lymphoma versus non-lymphoma, ePARR had 92% and 92% sensitivity and specificity on FFPE with 92% accuracy, 85% sensitivity from flow cytometry pellets (non-lymphoma was not evaluated to calculate specificity) with 85% accuracy, and 100% and 100% sensitivity and specificity for FNA with 100% accuracy. Stringent quality control criteria decreased assay success rate without significant performance improvement. Performance metrics were lower in most cases for discrimination of B- or T-cell versus non-B- or non-T-cell samples than for lymphoma versus non-lymphoma. CONCLUSIONS AND CLINICAL IMPORTANCE: These benchmarking data facilitate effective interpretation and application of PARR assays in multiple sample types.

Survival associated with cerebrospinal fluid analysis in downer adult dairy cows: A retrospective study (2006-2014).

BACKGROUND: Threshold values for total nucleated cell count (TNCC) and protein concentration in cerebrospinal fluid (CSF) of downer dairy cows suggestive of a spinal cord lesion were recently published. OBJECTIVES: Determine short- and long-term survival of downer cows that underwent CSF analysis using the reported threshold values. Evaluate the prognostic value of these threshold values to predict short- and long-term survival. ANIMALS: Two hundred and fourteen downer adult dairy cows that underwent CSF analysis during hospitalization at the Centre Hospitalier Universitaire Vétérinaire (CHUV) of the Université de Montréal. METHODS: Retrospective study. Medical records of downer adult dairy cows presented to the hospital between January 2006 and October 2014 for which CSF analysis results were available were studied. Short-term (discharge from hospital) and long-term (completion of lactation) survival were determined and compared in accordance with CSF TNCC and protein concentration, using a Chi-square test. RESULTS: Cows with CSF TNCC and/or protein concentration above the threshold values had a significantly lower short-term survival rate (P = .02). The odds of nonsurvival of cows with one or both CSF values above the threshold values was 2.16 times higher than the odds for cows with values under the threshold values. CSF TNCC >4.5 cells/µL had sensitivity and specificity of 17.3% (95% CI: 10.7%-25.7%) and 92.3% (95% CI: 85.4%-96.6%), respectively, for predicting short-term nonsurvival. CSF protein concentration >0.39 g/L had sensitivity and specificity of 20.9% (95% CI: 13.7%-29.7%) and 91.4% (95% CI: 84.2%-96.0%), respectively. CONCLUSIONS: CSF analysis above threshold values used in this study is associated with increased odds of short-term nonsurvival.

Long-term effectiveness of accelerated hepatitis B vaccination schedule in drug users.

OBJECTIVES: We demonstrated the effectiveness of an accelerated hepatitis B vaccination schedule in drug users. METHODS: We compared the long-term effectiveness of accelerated (0-1-2 months) and standard (0-1-6 months) hepatitis B vaccination schedules in preventing hepatitis B virus (HBV) infections and anti-hepatitis B (anti-HBs) antibody loss during 2-year follow-up in 707 drug users (HIV and HBV negative at enrollment and completed 3 vaccine doses) from February 2004 to October 2009. RESULTS: Drug users in the accelerated schedule group had significantly lower HBV infection rates, but had a similar rate of anti-HBs antibody loss compared with the standard schedule group over 2 years of follow-up. No chronic HBV infections were observed. Hepatitis C positivity at enrollment and age younger than 40 years were independent risk factors for HBV infection and antibody loss, respectively. CONCLUSIONS: An accelerated vaccination schedule was more preferable than a standard vaccination schedule in preventing HBV infections in drug users. To overcome the disadvantages of a standard vaccination schedule, an accelerated vaccination schedule should be considered in drug users with low adherence. Our study should be repeated in different cohorts to validate our findings and establish the role of an accelerated schedule in hepatitis B vaccination guidelines for drug users.

Customization of Advia 120 thresholds for canine erythrocyte volume and hemoglobin concentration, and effects on morphology flagging results.

This study sought to develop customized morphology flagging thresholds for canine erythrocyte volume and hemoglobin concentration [Hgb] on the ADVIA 120 hematology analyzer; compare automated morphology flagging with results of microscopic blood smear evaluation; and examine effects of customized thresholds on morphology flagging results. Customized thresholds were determined using data from 52 clinically healthy dogs. Blood smear evaluation and automated morphology flagging results were correlated with mean cell volume (MCV) and cellular hemoglobin concentration mean (CHCM) in 26 dogs. Customized thresholds were applied retroactively to complete blood (cell) count (CBC) data from 5 groups of dogs, including a reference sample group, clinical cases, and animals with experimentally induced iron deficiency anemia. Automated morphology flagging correlated more highly with MCV or CHCM than did blood smear evaluation; correlation with MCV was highest using customized thresholds. Customized morphology flagging thresholds resulted in more sensitive detection of microcytosis, macrocytosis, and hypochromasia than default thresholds.

Adaptation des seuils d'Advia 120 pour le volume d'érythrocytes et la concentration d'hémoglobines des chiens et les effets sur le signalement des résultats de la morphologie. Cette étude a cherché à développer des seuils de signalement adaptés à la morphologie pour le volume des érythrocytes et la concentration d'hémoglobines [Hgb] des chiens sur l'analyseur d'hématologie ADVIA 120; à comparer le signalement automatique de la morphologie avec les résultats de l'évaluation microscopique des frottis sanguins; et à examiner les effets des seuils adaptés sur les résultats de signalement de la morphologie. Des seuils adaptés ont été déterminés à l'aide de données de 52 chiens cliniquement en santé. L'évaluation des frottis sanguins et les résultats de signalement automatiques de la morphologie ont été corrélés avec le volume cellulaire moyen (VCM) et la concentration d'hémoglobines cellulaires moyennes (CHCM) chez 26 chiens. Les seuils adaptés ont été appliqués rétroactivement à des données d'hémogramme provenant de 5 groupes de chiens, y compris un groupe de référence, de cas cliniques et d'animaux avec une anémie ferriprive induite expérimentalement. Il y avait une corrélation supérieure du signalement automatique de la morphologie avec le VCM ou le CHCM par rapport à l'évaluation des frottis sanguins; la corrélation avec le VCM était supérieure en utilisant des seuils adaptés. Des seuils de signalement adaptés à la morphologie ont produit une détection plus sensible de la microcytose, de la macrocytose et de l'hypochromasie que les seuils par défaut.(Traduit par Isabelle Vallières).

Real-time polymerase chain reaction detection of asymptomatic Clostridium difficile colonization and rising C. difficile-associated disease rates.

OBJECTIVE: To evaluate the accuracy of real-time polymerase chain reaction (PCR) for Clostridium difficile-associated disease (CDAD) detection, after hospital CDAD rates significantly increased following real-time PCR initiation for CDAD diagnosis. DESIGN: Hospital-wide surveillance study following examination of CDAD incidence density rates by interrupted time series design. SETTING: Large university-based hospital. PARTICIPANTS: Hospitalized adult patients. METHODS: CDAD rates were compared before and after real-time PCR implementation in a university hospital and in the absence of physician and infection control practice changes. After real-time PCR introduction, all hospitalized adult patients were screened for C. difficile by testing a fecal specimen by real-time PCR, toxin enzyme-linked immunosorbent assay, and toxigenic culture. RESULTS: CDAD hospital rates significantly increased after changing from cell culture cytotoxicity assay to a real-time PCR assay. One hundred ninety-nine hospitalized subjects were enrolled, and 101 fecal specimens were collected. C. difficile was detected in 18 subjects (18%), including 5 subjects (28%) with either definite or probable CDAD and 13 patients (72%) with asymptomatic C. difficile colonization. CONCLUSIONS: The majority of healthcare-associated diarrhea is not attributable to CDAD, and the prevalence of asymptomatic C. difficile colonization exceeds CDAD rates in healthcare facilities. PCR detection of asymptomatic C. difficile colonization among patients with non-CDAD diarrhea may be contributing to rising CDAD rates and a significant number of CDAD false positives. PCR may be useful for CDAD screening, but further study is needed to guide interpretation of PCR detection of C. difficile and the value of confirmatory tests. A gold standard CDAD diagnostic assay is needed.