[Evaluation of interventions during the COVID-19 pandemic: development of a model based on subpopulations with different contact rates]. / Evaluación de intervenciones durante la pandemia COVID-19: desarrollo de un modelo basado en subpoblaciones con distintas tasas de contacto.

Although multiple attempts have been made to mathematically model the current epidemic of SARS-CoV-2, the causative agent of coronavirus disease 2019 (COVID-19), few models have been conceived as accessible interactive tools for users from various backgrounds. The goal of this study was to develop a model that took into account the heterogeneity in contact rates within the population and to implement it in an accessible application allowing to estimate the impact of possible interventions based on available information. An extended version of the Susceptible-Exposed-Infected-Resistant (SEIR) model, named SEIR-HL, was developed, assuming a population divided into two subpopulations, with different contact rates. Additionally, a formula for the calculation of the basic reproduction number (R0) for a population divided into n subpopulations was proposed, where the contact rates for each subpopulation can be distinguished according to contact type or context. The predictions made by SEIR-HL were compared to those of SEIR, showing that the heterogeneity in contact rates can dramatically affect the dynamics of simulations, even when run from the same initial conditions and with the same parameters. SEIR-HL was used to predict the effect on the epidemic evolution of the displacement of individuals from high-contact positions to low-contact positions. Lastly, by way of example, SEIR-HL was applied to the analysis of the SARS-CoV-2 epidemic in Argentina and an example of the application of the R0 formula was also developed. Both the SEIR-HL model and an R0 calculator were computerized and made available to the community.

High Substance Use and HIV Risk Behavior Among Young Argentine Men Who Have Sex with Men.

In the United States young men who have sex with men have higher rates of substance use, higher HIV incidence, and less frequent HIV testing than their heterosexual counterparts and older MSM. Less is known about comparable populations in Latin America. As part of an epidemiological study, MSM were recruited through Respondent Driven Sampling in the metropolitan area of Buenos Aires, Argentina and answered a computerized behavioral survey. From the total of 500 MSM enrolled, a sub-sample of 233 aged 18-25 was analyzed. The sample was concentrated among lower socioeconomic strata, and only 16% identified as gay. Nearly half reported male, female, and transvestite sexual partners. Reported substance use was widespread ranging from 61% for marijuana to 20% for pasta base (cocaine sulfate). Seventy percent of the sample had never been tested for HIV infection; 3% tested positive for HIV and 8% for syphilis during the study.

High Frequency of Illegal Drug Use Influences Condom Use Among Female Transgender Sex Workers in Argentina: Impact on HIV and Syphilis Infections.

The high prevalence of HIV and syphilis found among female transgender sex workers (FTSWs) in Argentina calls for the study of factors leading to negative health consequences. Given the particular characteristics observed in this population (high marginalization, school dropout, and low adherence to healthcare services), we explored the association of several socio-demographic characteristics with syphilis and HIV infections, and the determinants of condom use. This study revealed that FTSWs from Argentina were exposed to several risk factors decreasing thus their ability to negotiate condom use and leading to increased risk for transmission of HIV and other sexually transmitted infections (STIs). Strategies to reduce HIV and syphilis in this population should consider interventions aimed at decreasing violence and substance use which appear to be the most important determinants. Results of this study will contribute to the global information among FTSWs.

HIV testing practices among men who have sex with men in Buenos Aires, Argentina.

The objective of the study was to explore HIV-testing practices among men who have sex with men (MSM) in Buenos Aires, Argentina, in light of current international health guidelines that recommend frequent HIV testing for MSM who engage in high-risk behavior. Participants, who were recruited using respondent-driven sampling (RDS), were 500 mostly young, nongay-identified MSM of low socioeconomic status, high levels of unemployment, living mainly in the less-affluent areas surrounding Buenos Aires, and lacking health insurance. They provided blood samples for HIV testing and responded to a Computer Assisted Self Interview. Fifty-two percent had never been tested for HIV, and 20% had been tested only once; 17% were found to be HIV infected, of whom almost half were unaware of their status. Main reasons for never having tested previously were: not feeling at risk, fear of finding out results, and not knowing where to get tested. Among those previously tested, men had been tested a median of 2 times with their most recent test having occurred a median of 2.7 years prior to study enrollment. Of those who had not tested positive before entering the study, only 41% returned for their results. HIV testing was infrequent and insufficient for early detection of infection, entry into treatment, and protection of sexual partners. This was particularly the case among nongay-identified MSM. Testing campaigns should aim to help MSM become aware of their risk behavior, decrease fear of testing by explaining available treatment resources and decreasing the stigma associated with HIV, and by publicizing information about free and confidential testing locations. Rapid HIV testing should be made available to eliminate the need for a return visit and make results immediately available to individuals who are tested.

The Role of MicroRNAs in HIV Infection.

MicroRNAs (miRNAs), a class of small, non-coding RNAs, play a pivotal role in regulating gene expression at the post-transcriptional level. These regulatory molecules are integral to many biological processes and have been implicated in the pathogenesis of various diseases, including Human Immunodeficiency Virus (HIV) infection. This review aims to cover the current understanding of the multifaceted roles miRNAs assume in the context of HIV infection and pathogenesis. The discourse is structured around three primary focal points: (i) elucidation of the mechanisms through which miRNAs regulate HIV replication, encompassing both direct targeting of viral transcripts and indirect modulation of host factors critical for viral replication; (ii) examination of the modulation of miRNA expression by HIV, mediated through either viral proteins or the activation of cellular pathways consequent to viral infection; and (iii) assessment of the impact of miRNAs on the immune response and the progression of disease in HIV-infected individuals. Further, this review delves into the potential utility of miRNAs as biomarkers and therapeutic agents in HIV infection, underscoring the challenges and prospects inherent to this line of inquiry. The synthesis of current evidence positions miRNAs as significant modulators of the host-virus interplay, offering promising avenues for enhancing the diagnosis, treatment, and prevention of HIV infection.

HIV knowledge and beliefs among men who have sex with men (MSM) in Buenos Aires, Argentina.

Five hundred men who have sex with men (MSM), recruited through respondent driven sampling in Buenos Aires, Argentina, were interviewed in order to assess knowledge and beliefs about HIV infection. The mean proportion of HIV correct knowledge answers was 62 %; however participants whose sexual partners in the prior year included women (MSM&W) had lower frequencies of correct answers than participants with no women partners. Men with previous HIV testing experience and those who were HIV positive had higher HIV knowledge. In relation to HIV beliefs, less than half of participants responded correctly to each of the scenarios presented. Accurate answers for all items were more likely among those who only have sex with men. Men have basic HIV knowledge but also many misconceptions about transmission and prevention. Furthermore, MSM&W have less information than those who are exclusively MSM, probably related to the fact that information campaigns specifically targeted gay identified men.

High prevalence of substance use among men who have sex with men in Buenos Aires, Argentina: implications for HIV risk behavior.

Five hundred gay and other men who have sex with men (G&MSM) from Buenos Aires, Argentina completed an assessment regarding substance use and sexual behavior. During the past 2 months, 78 % of participants consumed alcohol and 61 % drugs. Over 20 % of participants reporting alcohol, marijuana, cocaine sulfate, or tranquilizer use, did so daily. Heavy alcohol use was more likely among participants with greater mood reactivity (AOR = 1.64) and less likely among those who identified as gay (AOR = 0.38). Weekly drug use was less likely among older (AOR = 0.98), and gay-identified participants (AOR = 0.50), but more likely among participants with greater mood reactivity (AOR = 1.49). Drug use was correlated with unprotected anal and vaginal intercourse with men, women, and transvestites among non-gay identified participants (r = 0.22). Findings highlight the need to reduce substance use and sexual risk behavior in this population.

High frequency of Nichols-like strains and increased levels of macrolide resistance in Treponema pallidum in clinical samples from Buenos Aires, Argentina.

Globally, 94% of Treponema pallidum subsp. pallidum (TPA) clinical strains belong to the SS14-like group and 6% to the Nichols-like group, with a prevalence of macrolide resistance of 90%. Our goal was to determine whether local TPA strain distribution and macrolide resistance frequency have changed significantly since our last report, which revealed that Buenos Aires had a high frequency of Nichols-like strains (27%) and low levels of macrolide resistance (14%). Swab samples from patients with suspected syphilis were collected during 2015-2019 and loci TP0136, TP0548, TP0705 were sequenced in order to perform multilocus sequence typing. Strains were classified as Nichols-like or SS14-like. The presence of macrolide resistance-associated mutations was determined by examination of the 23S rDNA gene sequence. Of 46 typeable samples, 37% were classified as Nichols-like and 63% as SS14-like. Macrolide resistance prevalence was 45.7%. Seven allelic profiles were found, five were SS14-like and two were Nichols-like. The frequency of Nichols-like strains increased between studies (26.8% vs. 37%, p = 0.36). A dramatic increase was found in the frequency of macrolide resistant strains between studies (14.3% vs. 45.7%, p = 0.005). Our results are in agreement with international trends and underscore the need to pursue further TPA molecular typing studies in South America.

SARS-CoV-2-Specific IgG and IgA response in maternal blood and breastmilk of vaccinated naïve and convalescent lactating participants.

Background: Recent studies have shown the presence of SARS-CoV-2-specific antibodies in the milk of breastfeeding mothers vaccinated with mRNA and convalescent. However, limited information is available in lactating women receiving other vaccine platforms used in developing countries, such as the inactivated SARS-CoV-2 vaccine BBIBP-CorV (Sinopharm) and the non-replicating adenovirus vaccines Sputnik V (Gamaleya Institute) and ChAdOx1-S (Oxford AstraZeneca). Methods: Here, we evaluated anti-SARS-CoV-2 IgG and IgA levels in both serum and milk samples using a longitudinal and a cross-sectional cohort of 208 breastfeeding vaccinated women from Argentina with or without previous SARS-CoV-2 infection. Results: The analysis showed that IgA levels remain constant in serum and milk of breastfeeding mothers between the first and second doses of vector-based vaccines (Sputnik V and ChAdOx1-S). After the second dose, anti-spike IgA was found positive in 100% of the serum samples and in 66% of breastmilk samples. In addition, no significant differences in milk IgA levels were observed in participants receiving BBIBP-CorV, Sputnik V or ChAdOx1-S. IgG levels in milk increased after the second dose of vector-based vaccines. Paired longitudinal samples taken at 45 and 120 days after the second dose showed a decrease in milk IgG levels over time. Study of IgA levels in serum and milk of vaccinated naïve of infection and vaccinated-convalescent breastfeeding participants showed significantly higher levels in vaccinated-convalescent than in participants without previous infection. Conclusion: This study is relevant to understand the protection against SARS-CoV-2 by passive immunity in newborns and children who are not yet eligible to receive vaccination.

Multilocus sequence typing of Treponema pallidum pallidum in children with acquired syphilis by nonsexual contact.

Background: There are scarce data of Treponema pallidum subsp. pallidum (TPA) characterization in children with syphilis. Nonsexually acquired transmission (NSAT) of TPA is possible in infants through close contact. Methods: A descriptive study in five families with NSAT of syphilis was conducted. Polymerase chain reaction detection of TPA in pediatric index cases (n = 6) and their relatives (n = 44) were conducted followed by multilocus sequence typing (MLST). Results: TPA was detected in swab samples in 16 cases and 12 were characterized by MLST. Nichols lineage was identified in two of five families and SS14-lineage in three of five. In four families, MLST profiles linked index cases to relatives. Conclusion: This is the first report of TPA characterization in children infected by NSAT.

Syphilis is a disease caused by the bacterium Treponema pallidum subsp. pallidum (TPA). Although it is considered a sexually transmitted disease, syphilis can also be transmitted by nonsexual close contact with active lesions. There are clinical reports of this route of transmissions in children; however, there are no molecular characterizations of TPA in this population. A multidisciplinary study (epidemiological, clinical, social and molecular) was performed in six children from five families with clinical diagnosis of nonsexually transmitted syphilis. As a result, 18 infected persons were detected. In 16 individuals the presence of the bacterium genetic material was confirmed by molecular biology techniques, and in 12, its strain was analyzed. When we compared the data, we observed that in four families, the child's strain coincided with the one found in close contact, while in one family, this could not be determined. To our knowledge, this is the first report of TPA characterization in children, which underscore the importance of including molecular biology techniques in complex clinical scenarios such as these.

Viral hepatitis and Treponema pallidum prevalence in persons who underwent premarital blood tests in Argentina.

The objective of this study was to estimate the prevalence of different serological markers of hepatitis A, B and C viruses and Treponema pallidum among the adult population of Argentina. To achieve this, adults who attended health services for premarital exams (which are mandatory and includes screening for syphilis) were recruited. A cross-sectional study was designed with a cluster sampling strategy. Couples who attended selected health services for premarital screening between 2013 and 2014 in Buenos Aires, Cordoba, Mendoza and Santa Fe provinces were included. A total of 3833 individuals were recruited. Anti-HAV prevalence was 63.9%, anti-HCV 0.3%, anti-HBc (without HBsAg) 1.9%, HBsAg 0.3%, and T pallidum 0.8%. Anti-HAV was higher among older participants, foreigners and those from the lower strata. HBV increased with age and was higher among foreigners and those with lower formal educational level. Anti-HCV frequency increased with age. Premarital screening of viral hepatitis could constitute an instance of diagnosis, vaccination and inclusion in care of those in need. Results from this study will allow the national hepatitis programs to design public policies in order to diminish the impact of these infections on the population.

Human immunodeficiency virus and tuberculosis in Argentina: prevalence, genotypes and risk factors.

The objective of this study was to determine the prevalence and genetic variability of human immunodeficiency virus type 1 (HIV-1) and other sexually transmitted infections (STIs) among 205 patients with clinical diagnosis of tuberculosis (TB) in Buenos Aires in 2001. Infections with hepatitis B virus (HBV), HIV-1, hepatitis C virus (HCV), Treponema pallidum and human T-cell lymphotropic virus types I/II were diagnosed in 37/187 (19.8 %), 35/205 (17.1 %), 22/187 (11.8 %), 13/187 (7.0 %) and 4/181 (2.2 %) patients, respectively. Almost one in three participants (33.1 %) presented at least one infection in addition to TB. Multiresistance to TB drugs (isoniazid plus rifampicin) was detected in the isolates recovered from three patients. Injecting drug use was detected as the main risk factor for HIV, HBV and HCV infections. Of ten patients who died, eight were infected with HIV. HIV genetic characterization showed the presence of two different subtypes. Env subtype F was found in 13/24 samples (54.2 %) and subtype B in 11/24 samples (45.8 %) by heteroduplex mobility assay. Sequencing of the protease/RT region was performed in ten samples: three were characterized as subtype B and seven as B/F recombinants by bootscanning analysis. Phylogenetic analysis of four full-length sequences showed that three were the circulating recombinant form CRF12_BF. The results of this study suggest an urgent need to detect HIV infection in high-risk groups to prevent future HIV transmission as well as morbidity and mortality associated with TB by providing highly active antiretroviral therapy (HAART) and/or TB treatment. Collaboration between TB and HIV programmes seems to be the best approach to decrease the incidence of these diseases, especially in high-prevalence HIV settings.

Comparison of four commercial screening assays for the diagnosis of human T-cell lymphotropic virus types 1 and 2.

Serological assays for human T-cell lymphotropic virus types 1 and 2 (HTLV-1/2) are widely used in routine screening of blood donors. The aim of this study was to compare the performance of four commercial screening assays for HTLV-1/2 infection frequently used in South America. A total of 142 HTLV-1 and HTLV-2 seropositive and 336 seronegative samples were analyzed by using four commercial tests (BioKit, Vironostika, Murex and Fujirebio). These tests are commonly used for HTLV-1/2 detection in blood banks in Argentina. A nested-PCR was used as the reference standard. The most sensitive tests for HTLV-1/2 were Fujirebio and Biokit (98.6%) followed by Murex (97.2%) and Vironostika (96.5%). The most specific test was Murex (99.7%), followed by Biokit (97.0%), Fujirebio (95.8%), and Vironostika (92.9%). The kappa index of agreement was higher for Murex (kappa=0.97), followed by BioKit (kappa=0.94), Fujirebio (kappa=0.92), and Vironostika (kappa=0.86). The highest index of agreement was shown by Murex test while Vironostika had the lowest performance. Of the four tests evaluated, only the Vironostika assay is approved by the Food and Drug Administration. These results should be considered for choosing the most accurate serological screening assays in order to obtain an optimal efficiency of the current algorithm for HTLV-1/2 diagnosis.

Evaluation of the utility of a rapid test for syphilis at a sexually transmitted disease clinic in Buenos Aires, Argentina.

Even though syphilis can be easily diagnosed by simple and low-cost laboratory methods, it continues to be an important health problem. Rapid tests (RT) for the detection of treponemal antibodies can facilitate earlier diagnosis, access to treatment and linkage to care. The aim of this study was to analyse the usefulness of the incorporation of a RT in the detection of patients infected with T. pallidum in a sexually-transmitted disease (STD) clinic. Between March and December 2015, a syphilis RT was offered to patients who spontaneously attended the clinic. Conventional serology testing was additionally indicated to every participant. The RT for syphilis was offered to 1887 patients, of whom 31.1% agreed to get tested. VDRL test was performed in 84.0% of patients that were also tested with syphilis RT, with a significantly higher frequency observed among participants with reactive RT (94.3% vs. 79.8%, p < 0.001). These results showed that 33.7% of the participants were reactive for the RT and 27.0% were reactive for the VDRL test. Both tests were reactive in 24.9% and non-reactive in 64.3%. A high prevalence of active syphilis was detected in patients attending the clinic. The use of a syphilis RT had a positive impact, which in combination with the VDRL test increased the number of patients that were effectively diagnosed.

High genetic variability of HIV-1 in female sex workers from Argentina.

BACKGROUND: A cross-sectional study on 625 Female Sex Workers (FSWs) was conducted between 2000 and 2002 in 6 cities in Argentina. This study describes the genetic diversity and the resistance profile of the HIV-infected subjects. RESULTS: Seventeen samples from HIV positive FSWs were genotyped by env HMA, showing the presence of 9 subtype F, 6 subtype B and 2 subtype C. Sequence analysis of the protease/RT region on 16 of these showed that 10 were BF recombinants, three were subtype B, two were subtype C, and one sample presented a dual infection with subtype B and a BF recombinant. Full-length genomes of five of the protease/RT BF recombinants were also sequenced, showing that three of them were CRF12_BF. One FSW had a dual HIV-1 infection with subtype B and a BF recombinant. The B sections of the BF recombinant clustered closely with the pure B sequence isolated from the same patient. Major resistance mutations to antiretroviral drugs were found in 3 of 16 (18.8%) strains. CONCLUSION: The genetic diversity of HIV strains among FSWs in Argentina was extensive; about three-quarters of the samples were infected with diverse BF recombinants, near twenty percent had primary ART resistance and one sample presented a dual infection. Heterosexual transmission of genetically diverse, drug resistant strains among FSWs and their clients represents an important and underestimated threat, in Argentina.

Buenos Aires cohort of men who have sex with men: prevalence, incidence, risk factors, and molecular genotyping of HIV type 1.

The prevalence, incidence, risk factors, and molecular genotyping of HIV-1 infection among men who have sex with men (MSM) were assessed through a prospective cohort study. The study was conducted in Buenos Aires from February 2003 to December 2004. Sociodemographic, sexual risk behavior data, and blood samples for HIV testing were collected at baseline and at 6 and 12 months. Cox regression analysis was applied to determine risk factors associated with HIV seroconversion. HIV-positive samples were analyzed by partial (pro/RT) and full-length genome sequencing. Of 811 HIV-negative participants evaluated at baseline, 327 volunteers that fulfilled the inclusion criteria were enrolled. Retention rates at 6 and 12 months were 97.2% and 91.5%, respectively. Twelve MSM seroconverted for HIV infection [incidence rate = 3.9 (95% CI = 2.0-6.7) per 100 person-years]. HIV seroconversion was associated with a greater number of different sexual contacts in the preceding 6 months (> or =10, hazard ratio = 3.3, 95% CI: 1.1-10.4). By partial pro/RT genotyping analysis, 83% HIV-positive samples were subtype B and 17% samples were BF recombinants, most of these being unique recombinant forms. This study describes for the first time the recruitment and follow-up of a cohort of MSM in Argentina. Retention rates and HIV incidence rate were high. These data should be considered as a promising potential population for HIV vaccine trials.

Genomic characterization and molecular evolution analysis of subtype B and BF recombinant HIV-1 strains among Argentinean men who have sex with men reveal a complex scenario.

Currently, data on HIV-1 circulating strains among men who have sex with men (MSM) in Argentina is scarce. In South America, the distribution and the prevalence of BF recombinants are dissimilar and exhibit an underappreciated heterogeneity of recombinant structures. Here, we studied for the first time the genetic diversity of HIV-1 BF recombinants and their evolution over time through in-depth phylogenetic analysis and multiple recombination detection methods involving 337 HIV-1 nucleotide sequences (25 near full-length (NFL) and 312 partial pol gene) obtained from Argentinean MSM. The recombination profiles were studied using multiple in silico tools to characterize the genetic mosaicism, and phylogenetic approaches to infer their relationships. The evolutionary history of BF recombinants and subtype B sequences was reconstructed by a Bayesian coalescent-based method. By phylogenetic inference, 81/312 pol sequences clustered within BF clade. Of them, 46 sequences showed a genetic mosaic with CRF12_BF-like patterns, including plausible second-generation recombinants. Other CRFs_BF like (CRF17, 28, 29, 39, 42, 44, 47) and probable URFs_BF were less frequently found. Phylogenetic and recombination analyses on NFL sequences allowed a meticulous definition of new BF mosaics of genomic patterns. The Bayesian analyses pointed out quite consistent onset dates for the CRFs_BF clade based on B and F gene datasets (~1986 and ~1991 respectively). These results indicate that the CRFs_BF variants have been circulating among Argentinean MSM for about 30 years. This study reveals, through growing evidence showing the importance of MSM in the dynamics of the HIV-1 epidemic in Argentina, the coexistence of CRF12_BF-like and high diversity of strains exhibiting several BF mosaic patterns, including non-reported URFs that may reflect active clusters as potential intervention targets to hinder HIV-1 transmission.

Molecular typing of Treponema pallidum isolates from Buenos Aires, Argentina: Frequent Nichols-like isolates and low levels of macrolide resistance.

A total of 54 clinical samples, including genital lesion swabs, whole blood and cerebrospinal fluid from patients diagnosed with syphilis were collected in 2006 and in 2013 in Buenos Aires, Argentina. Treponemal DNA was detected in 43 of the analyzed samples (79.6%) and further analyzed using Sequencing-based molecular typing (SBMT) and Enhanced CDC-typing (ECDCT). By SBMT, 10 different Treponema pallidum subsp. pallidum (TPA) genotypes were found, of which six were related to the TPA SS14 strain, and four to the TPA Nichols strain. The 23S rRNA gene was amplified in samples isolated from 42 patients, and in six of them (14.3%), either the A2058G (four patients, 9.5%) or the A2059G (two patients, 4.8%) mutations were found. In addition to Taiwan, Madagascar and Peru, Argentina is another country where the prevalence of Nichols-like isolates (26.8%) is greater than 10%.

Evaluación de intervenciones durante la pandemia COVID-19: desarrollo de un modelo basado en subpoblaciones con distintas tasas de contacto / Evaluation of interventions during the COVID-19 pandemic: development of a modelbased on subpopulations with different contact rates

Resumen Si bien se han realizado múltiples intentos de modelar matemáticamente la pande-mia de la enfermedad por coronavirus 2019 (COVID-19), causada por SARS-CoV-2, pocos modeloshan sido pensados como herramientas interactivas accesibles para usuarios de distintos ámbitos.El objetivo de este trabajo fue desarrollar un modelo que tuviera en cuenta la heterogeneidadde las tasas de contacto de la población e implementarlo en una aplicación accesible, que per-mitiera estimar el impacto de posibles intervenciones a partir de información disponible. Sedesarrolló una versión ampliada del modelo susceptible-expuesto-infectado-resistente (SEIR),denominada SEIR-HL, que asume una población dividida en dos subpoblaciones, con tasas decontacto diferentes. Asimismo, se desarrolló una fórmula para calcular el número básico dereproducción (R0) para una población dividida en n subpoblaciones, discriminando las tasas decontacto de cada subpoblación según el tipo o contexto de contacto. Se compararon las pre-dicciones del SEIR-HL con las del SEIR y se demostró que la heterogeneidad en las tasas decontacto puede afectar drásticamente la dinámica de las simulaciones, aun partiendo de lasmismas condiciones iniciales y los mismos parámetros. Se empleó el SEIR-HL para mostrar elefecto sobre la evolución de la pandemia del desplazamiento de individuos desde posiciones dealto contacto hacia posiciones de bajo contacto. Finalmente, a modo de ejemplo, se aplicó elSEIR-HL al análisis de la pandemia de COVID-19 en Argentina; también se desarrolló un ejemplode uso de la fórmula del R0. Tanto el SEIR-HL como una calculadora del R0fueron implementadosinformáticamente y puestos a disposición de la comunidad.

Abstract Although multiple attempts have been made to mathematically model the currentepidemic of SARS-CoV-2, the causative agent of coronavirus disease 2019 (COVID-19), fewmodels have been conceived as accessible interactive tools for users from various backgrounds.The goal of this study was to develop a model that took into account the heterogeneity incontact rates within the population and to implement it in an accessible application allowingto estimate the impact of possible interventions based on available information. An extendedversion of the Susceptible-Exposed-Infected-Resistant (SEIR) model, named SEIR-HL, was deve-loped, assuming a population divided into two subpopulations, with different contact rates.Additionally, a formula for the calculation of the basic reproduction number (R0) for a popula-tion divided into n subpopulations was proposed, where the contact rates for each subpopulationcan be distinguished according to contact type or context. The predictions made by SEIR-HLwere compared to those of SEIR, showing that the heterogeneity in contact rates can drama-tically affect the dynamics of simulations, even when run from the same initial conditions andwith the same parameters. SEIR-HL was used to predict the effect on the epidemic evolution ofthe displacement of individuals from high-contact positions to low-contact positions. Lastly, byway of example, SEIR-HL was applied to the analysis of the SARS-CoV-2 epidemic in Argentinaand an example of the application of the R0formula was also developed. Both the SEIR-HLmodel and an R0calculator were computerized and made available to the community.

High acceptability of rapid HIV self-testing among a diverse sample of MSM from Buenos Aires, Argentina.

INTRODUCTION: The objective of this study was to explore the acceptability of rapid HIV self-testing (RHST) among men who have sex with men (MSM). METHODS: During 2006-2009, a sample of 500 MSM was recruited through Respondent Driven Sampling for an HIV prevalence/incidence study. Attitude toward RHST was explored among HIV negative MSM. Data were weighted prior to analyses. RESULTS: Participants reported they were likely to buy RHST (74%), test themselves more frequently than they currently do (77%), and that the procedure would simplify testing (70%). Furthermore, 71% reported they would probably use it alone, 66% would use it with a steady partner, and 56% with a friend/partner. While a majority acknowledged that RHST use would deprive them of receiving counseling (61%), 74% declared they would go for help if they tested positive; 57% would use an RHST in order to avoid condoms. Probability of use surpassed 70% among gay and non-gay identified MSM as well as those with and without a previous HIV test. Those likely to buy RHST were older (p = 0.025) and more likely to identify as gay (p = 0.036). A total of 17% said they would think about killing themselves and 9% would attempt suicide if they tested positive. These MSM were more likely to be younger (p<0.001), with lower mood level (p<0.001) and greater feelings of loneliness (p = 0.026). CONCLUSIONS: The high acceptability of RHST found among MSM should encourage the authorities to consider the possibility of offering it for self-testing, as it can improve early diagnosis and prevention of future transmissions. However, further research is needed to understand how to best disseminate RHST among MSM who wish to use it and to offer support and linkage to care for those who test HIV-positive.