Entropic Effects on the Aqueous Microsolvation of Protonated Glycine and Protonated ß-Alanine. Hybrid Density Functional Theory Born-Oppenheimer Molecular Dynamics Studies.

Recent low-temperature infrared-based experimental studies provided information about the effects of aqueous microsolvation on the intramolecular hydrogen bond of protonated glycine and ß-alanine [J. Phys. Chem. A 2019, 123, 3355]. Here we address the temperature-dependent entropic effects on the aqueous microsolvation patterns of these protonated amino acids using the AAH+(H2O)n (n = 1-8) cluster model at 50 K and room temperature with Born-Oppenheimer molecular dynamics using a calibrated hybrid density functional. The CCOOH-Ow, N-Ow, and center-of-mass-Ow radial distribution functions provide accurate structural data and temperature-dependent water coordination numbers vs. solvation degree. The solvation patterns for protonated glycine at 50 K show structural features in agreement with previous static optimizations. However, entropic effects at room temperature play a crucial role in the evolution of the intramolecular HB strength vs. solvation degree for both protonated amino acids. With increasing hydration entropic effects favor the making of solvent hydrogen bond networks over full solvation of protonated glycine. At room temperature four water molecules are needed to build the first solvation shell for protonated glycine while five are required for protonated ß-alanine. A new statistical Cumulative Percentage of Structures (CPS) scheme is proposed; when the CPS data are analyzed in light of the empirical formula of Rozenberg et al. [Phys. Chem. Chem. Phys. 2000, 2, 2699] and the hydrogen bond relative strength (HBRS) criteria of Jeffrey [An Introduction to Hydrogen Bonding; Oxford University: 1997] we can provide a detailed molecular mechanism for the weakening of the intramolecular hydrogen bond based on the average dynamical structures, which clearly reveals the temperature dependence of this process. The new CPS-HBRS scheme proposed here can be utilized using any type of molecular dynamics trajectory (classical, BOMD, CPMD, etc.).

Ammonia Solvation vs Aqueous Solvation of Samarium Diiodide. A Theoretical and Experimental Approach to Understanding Bond Activation Upon Coordination to Sm(II).

Coordination-induced desolvation or ligand displacement by cosolvents and additives is a key feature responsible for the reactivity of Sm(II)-based reagent systems. High-affinity proton donor cosolvents such as water and glycols also demonstrate coordination-induced bond weakening of the O-H bond, facilitating reduction of a broad range of substrates. In the present work, the coordination of ammonia to SmI2 was examined using Born-Oppenheimer molecular dynamics simulations and mechanistic studies, and the SmI2-ammonia system is compared to the SmI2-water system. The coordination number and reactivity of the SmI2-ammonia solvent system were found to be similar to those of SmI2-water but exhibited an order of magnitude greater rate of arene reduction by SmI2-ammonia than by SmI2-water at the same concentrations of cosolvent. In addition, upon coordination of ammonia to SmI2, the Sm(II)-ammonia solvate demonstrates one of the largest degrees of N-H bond weakening reported in the literature compared to known low-valent transition metal ammonia complexes.

Differential activation of innate and adaptive lymphocytes during latent or active infection with Mycobacterium tuberculosis.

Most individuals infected with Mycobacterium tuberculosis (Mtb) have latent tuberculosis (TB), which can be diagnosed with tests (such as the QuantiFERON-TB Gold test [QFT]) that detect the production of IFN-γ by memory T cells in response to the Mtb-specific antigens 6 kDa early secretory antigenic target EsxA (Rv3875) (ESAT-6), 10 kDa culture filtrate antigen EsxB (Rv3874) (CFP-10), and Mtb antigen of 7.7 kDa (Rv2654c) (TB7.7). However, the immunological mechanisms that determine if an individual will develop latent or active TB remain incompletely understood. Here we compared the response of innate and adaptive peripheral blood lymphocytes from healthy individuals without Mtb infection (QFT negative) and from individuals with latent (QFT positive) or active TB infection, to determine the characteristics of these cells that correlate with each condition. In active TB patients, the levels of IFN-γ that were produced in response to Mtb-specific antigens had high positive correlations with IL-1ß, TNF-α, MCP-1, IL-6, IL-12p70, and IL-23, while the proinflammatory cytokines had high positive correlations between themselves and with IL-12p70 and IL-23. These correlations were not observed in QFT-negative or QFT-positive healthy volunteers. Activation with Mtb-soluble extract (a mixture of Mtb antigens and pathogen-associated molecular patterns [PAMPs]) increased the percentage of IFN-γ-/IL-17-producing NK cells and of IL-17-producing innate lymphoid cell 3 (ILC3) in the peripheral blood of active TB patients, but not of QFT-negative or QFT-positive healthy volunteers. Thus, active TB patients have both adaptive and innate lymphocyte subsets that produce characteristic cytokine profiles in response to Mtb-specific antigens or PAMPs. These profiles are not observed in uninfected individuals or in individuals with latent TB, suggesting that they are a response to active TB infection.

Pulmonary Histoplasmosis in a Referral Hospital in Mexico City.

Pulmonary histoplasmosis is caused by inhaling Histoplasma capsulatum. Less than 1% develops the disease. Risk factors in immunocompetent individuals are environmental exposures in endemic areas. The objective of this study is to determine the frequency, clinical, and microbiological characteristics in immunocompetent patients. A retrospective case series study of patients diagnosed with pulmonary histoplasmosis was performed in a respiratory care unit in Mexico City from 2000 to 2020. Each patient had bronchial lavage, and three patients underwent thoracoscopy for the lung tissue sample taken for the culture in Sabouraud Dextrose Agar. Twelve patients were identified, 8 males and 4 females; the predominant symptoms were fever (83%), dyspnea (75%), chest pain (66%), hemoptysis (41%), and weight loss (33%). The computed tomography of the chest showed the following findings: patchy consolidation 12 (100%), hilar adenopathy 6 (50%), pleural effusion 6 (50%), caverns 3 (25%), and solitary pulmonary nodule in one patient (8%). Histoplasma capsulatum was found in the culture of all twelve patients. The signs and symptoms of the disease are mediated by the immune status of the host. The clinical picture is often confused with systemic diseases. It is important to have a high degree of clinical suspicion to make a timely diagnosis.

Identificación de un brote de SARSCoV-2 (Covid-19) en un centro gerontológico de la Ciudad de México.

OBJECTIVE: To describe a Covid-19 outbreak in a gerontological center in Mexico City. MATERIAL AND METHODS: Cross-sectional study in older adults. The association of risk factors for dying from Covid-19 was analyzed using a multiple logistic regression model. RESULTS: One hundred and two elders with an average age of 82.5 ± 8.8 years were included. Fifty-five (54%) tested positive and 47 (46%) were negative for the new coronavirus. Using the multiple logistic regression model, people with frailty had an OR of 11.6 of dying from Covid-19 compared to robust people (p-value = 0.024). CONCLUSION: The Covid-19 outbreak was initially caused by a resident of the center and spread by cross infection. In vulnerable populations, early detection, isolation, and follow-up of contacts should be carried out, as well as the identification of risk factors in order to reduce the spread and mortality caused by SARSCoV-2.

Characteristics and mortality of Mexican patients with COVID-19 and mechanical ventilation.

INTRODUCTION: COVID-19-associated mortality in patients who require mechanical ventilation is unknown in the Mexican population. OBJECTIVE: To describe the characteristics of Mexican patients with COVID-19 who required mechanical ventilation. METHODS: Observational cohort study carried out in an intensive care unit from March 25 to July 17, 2020. Data were obtained from a prospective database and electronic medical records, and were analyzed with the chi-square test, Fisher's exact test or Mann-Whitney's U-test. RESULTS: One hundred patients required mechanical ventilation; median age was 56 years, 31 % were females and 97 % were Latin American. Most common comorbidities were obesity (36 %), diabetes (26 %), hypertension (20 %), and chronic or end-stage kidney disease (10 %). At the end of the analysis, 11 patients remained in the ICU, 31 had been discharged alive and 58 (65.2 %) died; survivors were younger, had lower scores on severity and organ dysfunction scales, lower levels of C-reactive protein at ICU admission, were less likely to receive hemodialysis and vasopressors, and had longer hospital and ICU stays. CONCLUSIONS: This study adds information on the presentation and results of SARS-CoV-2-infected patients who require mechanical ventilation.

INTRODUCCIÓN: La mortalidad por COVID-19 en quienes requieren ventilación mecánica se desconoce en la población mexicana. OBJETIVO: Describir las características de pacientes mexicanos con COVID-19 que requirieron ventilación mecánica. MÉTODOS: Estudio de cohorte observacional en una unidad de terapia intensiva, del 25 de marzo al 17 de julio de 2020. Los datos se obtuvieron de una base de datos prospectiva y de registros clínicos electrónicos; fueron analizados con c2, prueba exacta de Fisher o prueba U de Mann-Whitney. RESULTADOS: Cien pacientes recibieron ventilación mecánica, la edad media fue de 56 años, 31 % era del sexo femenino y 97 %, latinoamericano. Las comorbilidades más comunes fueron obesidad (36 %), diabetes (26 %), hipertensión (20 %) y enfermedad renal crónica o renal terminal (10 %). Al término del análisis, 11 pacientes permanecían en la UCI, 31 egresaron vivos y 58 (65.2 %) fallecieron; los sobrevivientes fueron más jóvenes, con menores puntuación en las escalas de gravedad y disfunción orgánica, menores niveles de proteína C reactiva al ingreso a la UCI, menor propensión a hemodiálisis, necesidad de, necesidad de vasopresores y con mayor estancia hospitalaria y en la UCI. CONCLUSIONES: Este estudio agrega información sobre la presentación y resultados de pacientes con ventilación mecánica infectados con SARS-CoV-2.

Solving the CH_{4}

Several types of experiments showed the existence of negative methane ions CH_{4}^{-} over a period of 50 years but the nature of this elusive species remains unknown. A benchmark study has shown that the experimentally observed species cannot be described by the attachment of an electron in the doublet ground state of CH_{4}^{-}. Here we find CH_{4}^{-} as being a metastable species in its lowest quartet spin state, a CH_{2}^{-}:H_{2} exciplex with three open shells lying ca. 10 eV above the methane singlet ground state but slightly below the dissociation fragments. The formation of charged high-spin exciplexes is a novel mechanism to explain small molecular anions with implications in a plethora of basic and applied research fields.

Experimental and Theoretical Studies on the Aqueous Solvation and Reactivity of SmCl2 and Comparison with SmBr2 and SmI2.

Water addition to Sm(II) has been shown to increase reactivity for both SmI2 and SmBr2. Previous work in our groups has demonstrated that this increase in reactivity can be attributed to coordination induced bond weakening enabling substrate reduction through proton-coupled electron transfer. The present work examines the interaction of water with samarium dichloride (SmCl2) and illustrates the importance of the Sm-X interaction and bond distance upon water addition critical for the reactivity of the reagent system. Born-Oppenheimer molecular dynamics simulations identify substantial variations among the reductants created in solution upon water addition to SmI2, SmBr2, and SmCl2 with the latter showing the least halide dissociation. This results in a lower water coordination number for SmCl2, creating a more powerful reducing system. As previously shown with the other SmX2-water systems, coordination-induced bond-weakening of the O-H bond of water bound to Sm(II) results in significant bond weakening. In the case of SmCl2, the bond weakening is estimated to be in the range of 83 to 88.5 kcal/mol.

Symmetric dissociation of the water molecule with truncation energy error. A benchmark study.

We use selected configuration interaction with truncation energy error (SCI-TEE) and CI by parts (CIBP) to study the symmetric dissociation of the water molecule with Roos' triple-ζ double polarization basis set and with the Dunning cc-pVTZ basis. The calculations comprise CISDTQ (CI-4x) through CI-8x for H2O at its equilibrium geometry (Req) and up to fifteen times Req. With the Dunning basis our SCI-TEE-8x energies differ from full CI by less than 0.01 mHartree (0.006 kcal mol-1) at all O-H distances, representing the best upper bounds for this system outside Req. We compare our results with those of other relevant ab initio methods finding good agreement with recent DMRG calculations. The non-parallelity error (NPE) for SCI-TEE-6x remains stable below 0.1 mHartree when moving from the Roos to the Dunning orbitals. For the present system, CBS energy errors at the experimental equilibrium geometry and at dissociation can accurately be evaluated as the difference between non-relativistic total electronic energies taken from the literature, and our SCI-TEE-8x energies obtained with Dunning's or Roos' orbitals. In both cases, the difference between CBS energy errors at the equilibrium geometry and dissociation is not smaller than 10 mH, showing that chemically accurate NPE values do not guarantee a chemically accurate potential energy surface.

Impact of strategic planning, organizational culture imprint and care bundles to reduce adverse events in the ICU.

OBJECTIVE: To evaluate the occurrence of adverse events during a multifaceted program implementation. DESIGN: Cross-sectional secondary analysis. SETTING: The respiratory-ICU of a large tertiary care center. PARTICIPANTS: Retrospectively collected data of patients admitted from 1 March 2010 to 28 February 2014 (usual care period) and from 1 March 2014 to 1 March 2017 (multifaceted program period) were used. INTERVENTIONS: The program integrated three components: (1) strategic planning and organizational culture imprint; (2) training and practice and (3) implementation of care bundles. Strategic planning redefined the respiratory-ICU Mission and Vision, its SWOT matrix (strengths, weaknesses, opportunities, threats) as well as its medium to long-term aims and planned actions. A 'Wear the Institution's T-shirt' monthly conference was given in order to foster organizational culture in healthcare personnel. Training was conducted on hand hygiene and projects 'Pneumonia Zero' and 'Bacteremia Zero'. Finally, actions of both projects were implemented. MAIN OUTCOME MEASURES: Rates of adverse events (episodes per 1000 patient/days). RESULTS: Out of 1662 patients (usual care, n = 981; multifaceted program, n = 681) there was a statistically significant reduction during the multifaceted program in episodes of accidental extubation ([Rate ratio, 95% CI] 0.31, 0.17-0.55), pneumothorax (0.48, 0.26-0.87), change of endotracheal tube (0.17, 0.07-0.44), atelectasis (0.37, 0.20-0.68) and death in the ICU (0.82, 0.69-0.97). CONCLUSIONS: A multifaceted program including strategic planning, organizational culture imprint and care protocols was associated with a significant reduction of adverse events in the respiratory-ICU.

Identificación de Mycobacterium bovis en pacientes con diagnóstico de tuberculosis pulmonar y extrapulmonar.

INTRODUCTION: In Mexico, there is an alarming increase in the number of cases of Mycobacterium bovis infection on pulmonary and extrapulmonary presentations. The lack of timely identification triggers complications and increases mortality. OBJECTIVE: To know the frequency of M. bovis infections in clinical samples of patients with tuberculosis in the mycobacteria laboratory of a reference hospital in Mexico City. METHOD: Prospective, descriptive study. Strains isolated from biological material were studied in Löwestein-Jensen and MGITI960 cultures. M. bovis was identified by amplifying the RD9 fragment with end-point polymerase chain reaction (PCR). RESULTS: Eight-hundred and fifty tuberculosis-diagnosed patients were included; in 441 cases, Mycobacterium tuberculosis was confirmed by positive culture (250 pulmonary, 65 ganglionic, 39 renal, 34 meningeal, 25 miliary, 14 pleural, 8 peritoneal, 4 bone and 2 pericardial cases). Forty-eight strains (10.8%) were typified as M. bovis by amplification of the RD9 fragment with end-point PCR. CONCLUSIONS: M. bovis is not currently thought of a causative agent of tuberculosis, which could be the cause of pharmacological treatment failure. In this study, the main extrapulmonary form was observed to be cervical lymphadenopathy.

INTRODUCCIÓN: En México existe un incremento alarmante de casos de infección pulmonar y extrapulmonar por Mycobacterium bovis. La falta de identificación oportuna deriva en complicaciones y eleva la mortalidad. OBJETIVO: Conocer la frecuencia de infecciones por Mycobacterium bovis en muestras clínicas de pacientes con tuberculosis, identificadas en el laboratorio de micobacterias en un hospital de concentración de la Ciudad de México. MÉTODO: Estudio prospectivo, descriptivo. Se estudiaron cepas aisladas de material biológico en cultivos Löwestein-Jensen y MGITI960. La identificación de Mycobacterium bovis se realizó mediante la amplificación del fragmento RD9 por PCR punto final. RESULTADOS: Se incluyeron 850 pacientes con diagnóstico de tuberculosis, en 441 casos se confirmó Mycobacterium tuberculosis por cultivo positivo (250 casos pulmonares, 65 ganglionares, 39 renales, 34 meníngeos, 25 miliares, 14 pleurales, ocho peritoneales, cuatro óseos y dos pericárdicos). Se tipificaron 48 cepas (10.8 %) como Mycobacterium bovis por amplificación del fragmento RD9 por PCR punto final. CONCLUSIONES: Actualmente no se piensa en Mycobacterium bovis como agente causal de tuberculosis, lo que pudiera ser la causa del fracaso del tratamiento farmacológico. En este estudio se observó que la principal forma extrapulmonar es la linfadenopatía cervical.

Experimental and Theoretical Studies on the Implications of Halide-Dependent Aqueous Solvation of Sm(II).

The addition of water to samarium(II) has been demonstrated to have a significant impact on the reduction of organic substrates, with the majority of research dedicated to the most widely used reagent, samarium diiodide (SmI2). The work presented herein focuses on the reducing capabilities of samarium dibromide (SmBr2) and demonstrates how the modest change in halide ligand results in observable mechanistic differences between the SmBr2-water and the SmI2-water systems that have considerable implications in terms of reactivity between the two reagents. Quantum chemical results from Born-Oppenheimer molecular dynamics simulations show significant differences between SmI2-water and SmBr2-water, with the latter displaying less dissociation of the halide, which results in a lower coordination number for water. Experimental results are consistent with computational results and demonstrate that the coordination sphere of SmBr2 is saturated at lower concentrations of water. In addition, coordination-induced bond-weakening of the O-H bond is demonstrably different for water bound to SmBr2, leading to an estimated O-H bond-weakening of at least 83 kcal/mol, nearly 10 kcal/mol larger than the bond-weakening observed in SmI2-H2O. Experimental results also demonstrate that the use of alcohols in place of water with SmBr2 leads to substrate reduction, albeit several orders of magnitude slower than for SmBr2-water. The difference in rates resulting from the change in proton donor is attributed to a rate-limiting proton-coupled electron transfer in SmBr2-water and a sequential electron transfer then proton transfer in SmBr2-alcohol systems, where electron transfer is rate-limiting.

Aqueous Solvation of SmI3: A Born-Oppenheimer Molecular Dynamics Density Functional Theory Cluster Approach.

We report the results of Born-Oppenheimer molecular dynamics (BOMD) simulations on the aqueous solvation of the SmI3 molecule and of the bare Sm3+ cation at room temperature using the cluster microsolvation approach including 37 and 29 water molecules, respectively. The electronic structure calculations were done using the M062X hybrid exchange-correlation functional in conjunction with the 6-31G** basis sets for oxygen and hydrogen. For the iodine and samarium atoms, the Stuttgart-Köln relativistic effective-core potentials were utilized with their associated valence basis sets. When SmI3 is embedded in the microsolvation environment, we find that substitution of the iodine ions by water molecules around Sm(III) cannot be achieved due to an insufficient number of explicit water molecules to fully solvate the four separate metal and halogen ions. Therefore, we studied the solvation dynamics of the bare Sm3+ cation with a 29-water molecule model cluster. Through the Sm-O radial distribution function and the evolution of the Sm-O distances, the present study yields a very tightly bound first rigid Sm(III) solvation shell from 2.3 to 2.9 Å whose integration leads to a coordination number of 9 water molecules and a second softer solvation sphere from 3.9 to 5 Å with 12 water molecules. No water exchange processes were found. The theoretical EXAFS spectrum is in excellent agreement with the experimental spectrum for Sm(III) in liquid water. The strong differences between the solvation patterns of Sm(III) vs Sm(II) are discussed in detail.

Hydration of CH3HgOH and CH3HgCl compared to HgCl2, HgClOH, and Hg(OH)2: A DFT microsolvation cluster approach.

We address the aqueous microsolvation of the CH3HgCl and CH3HgOH molecules using a stepwise hydration scheme including up to 33 water molecules and compare our results with the previously studied HgCl2, HgClOH, and Hg(OH)2 complexes. Optimized geometries and Gibbs free energies were obtained at the B3PW91/aug-RECP(Hg)-6-31G(d,p) level. At least 33 water molecules were required to build the first solvation shell around both methylmercury compounds. Optimized geometries were found having favorable interactions of water molecules with Hg, Cl, and the OH moiety. Born-Oppenheimer molecular dynamics simulations were performed on the largest CH3HgX(X = Cl, OH)-(H2O)33 clusters at the same level of theory. Born-Oppenheimer molecular dynamics simulations at T = 300 K (ca. 0.62 kcal/mol) revealed the presence of configurations with hydrogen-bonded networks that include the OH moiety in CH3HgOH and exclude both the Hg and Cl in CH3HgCl, favoring a clathrate-type structure around the methyl moiety. The comparison to the microsolvated HgClOH, Hg(OH)2, and HgCl2 molecules showed that, in all cases, the water molecules easily move away from Cl, thus supporting the idea that HgCl2 behaves as a non-polar solute. The theoretical (LIII edge) X-ray absorption near edge structure spectra are obtained and found in good agreement with experimental data, especially for the CH3HgCl species.

Multicentre propensity score-matched analysis of laparoscopic versus open surgery for T4 rectal cancer.

BACKGROUND: The use of laparoscopy for advanced-stage rectal cancer remains controversial. This study aimed to compare the operative and oncologic outcomes of laparoscopic (LAR) versus open anterior rectal resection (OAR) for patients with pT4 rectal cancer. METHODS: This is a multicenter propensity score matching (PSM) study of patients undergoing elective curative-intent LAR or OAR for pT4 rectal cancer (TNM stage II/III/IV) between 2005 and 2015. RESULTS: In total, 137 patients were included in the analysis. After PSM, demographic, clinical and tumor characteristics were similar between the 52 LAR and the 52 OAR patients. Overall, 52 tumors were located in the high rectum, 25 in the mid-rectum and 27 in the low rectum. Multivisceral resection was performed in 26.9% of LAR and 30.8% of OAR patients (p = 0.829). Conversion was required in 11 LAR patients (21.2%). The LAR group showed significantly shorter time to flatus (3.13 vs. 4.97 days, p = 0.001), time to regular diet (3.59 vs. 6.36 days, p < 0.0001) and hospital stay (15.49 vs. 17.96 days, p = 0.002) compared to the OAR group. The 90-day morbidity and mortality were not different between groups. In the majority of patients (85.6%), R0 resection was achieved. A complete mesorectal excision was obtained in 82.7% of LAR and 78.8% of OAR patients (p = 0.855). The 1-, 2- and 3-year overall survival rates were, respectively, 95.6, 73.8 and 66.7% for the LAR group and 86.7, 66.9 and 64.1% for the OAR group (p = 0.219). The presence of synchronous metastases (hazard ratio 2.26), R1 resection (HR 2.71) and lymph node involvement (HR 2.24) were significant predictors of overall survival. CONCLUSION: The present study suggests that LAR for pT4 rectal cancer can achieve good pathologic and oncologic outcomes similar to open surgery despite the risk of conversion. Moreover, laparoscopy offers the benefits of a faster recovery and a shorter hospital stay.

An Architecture for On-Line Measurement of the Tip Clearance and Time of Arrival of a Bladed Disk of an Aircraft Engine.

Safety and performance of the turbo-engine in an aircraft is directly affected by the health of its blades. In recent years, several improvements to the sensors have taken place to monitor the blades in a non-intrusive way. The parameters that are usually measured are the distance between the blade tip and the casing, and the passing time at a given point. Simultaneously, several techniques have been developed that allow for the inference-from those parameters and under certain conditions-of the amplitude and frequency of the blade vibration. These measurements are carried out on engines set on a rig, before being installed in an airplane. In order to incorporate these methods during the regular operation of the engine, signal processing that allows for the monitoring of those parameters at all times should be developed. This article introduces an architecture, based on a trifurcated optic sensor and a hardware processor, that fulfills this need. The proposed architecture is scalable and allows several sensors to be simultaneously monitored at different points around a bladed disk. Furthermore, the results obtained by the electronic system will be compared with the results obtained by the validation of the optic sensor.

Prevalence of HMTV in breast carcinomas and unaffected tissue from Mexican women.

BACKGROUND: Breast cancer is a complex multifactorial genetic disease. Among other factors, race and, to an even greater extent, viruses are known to influence the development of this heterogeneous disease. It has been reported that MMTV-like (HMTV) gene sequences with a 90 to 98% homology to mouse mammary tumor virus are found in several populations with a prevalence range of 0 to 74%. In the Mexican population, 4.2% of patients with breast cancer exhibit the presence of HMTV (MMTV-like) sequences. The aim of this study was to evaluate the presence and current prevalence of retroviral HMTV (MMTV-like) sequences in breast cancer in Mexican women. METHODS: We used nested PCR and real-time PCR with a TaqMan probe. As a positive control, we used the C3H MMTV strain inserted into pBR322 plasmid. To confirm that we had identified the HMTV sequences, we sequenced the amplicons and compared these sequences with those of MMTV and HMTV (GenBank AF033807 and AF346816). RESULTS: A total of 12.4% of breast tumors were HMTV-positive, and 15.7% of the unaffected tissue samples from 458 patients were HMTV-positive. A total of 8.3% of the patients had both HMTV-positive tumor and adjacent tissues. The HMTV-positive samples presented 98% similarity to the reported HMTV sequence. CONCLUSIONS: These results confirm that the HMTV sequence is present in breast tumors and non-affected tissues in the Mexican population. HMTV should be considered a prominent causative agent of breast cancer.