bluuebunny/crossref_metadata_2025_split huggingface dataset:
P1-S4.08 Population size estimates for men who have sex with men in Guatemala City using time location sampling and respondent driven sampling
Authors: Paz-Bailey G , Alvarez B , Miller W , Sabrina B , Barrington C , Kim A , Morales S , Chen S 
Published: July 2011

BackgroundMen who have sex with men (MSM) are highly vulnerable to HIV infection, but this population can be particularly difficult to reach in Central America due to stigma and violence. Knowing the size of populations at high risk for HIV and sexually transmitted infections (STI) is critical for informing prevention, care, and treatment programs. Simple approaches are needed to provide baseline estimates of the population size of MSM in Guatemala to advocate for appropriate resource allocation and programming. We compared population size estimates of MSM and transgender persons using capture-recapture linked to two differentsurveys that were developed concurrently using different sampling methodologies.MethodsCapture recapture methods for estimating population size were integrated into two probability-based surveys using respondent driven sampling (RDS) and time-location sampling (TLS); conducted simultaneously among MSM in Guatemala City from October to December 2010. Key chains were used as uUnique objects in the form ofand study key chains were distributed approximately 1-month prior to the surveys in venues known to be frequented by MSM. Duplicate participation was avoided by using the same team to distribute the key chains and administering a set of questions before handing the object. Participants in the RDS and TLS surveys were asked, as part of the study interview, whether they had received the key chain. We assigned the number of key chains distributed in venues as the first capture and the proportion of participants that reported receiving the key chain in the RDS or TLS survey as the second capture. By applying standardised formulas for estimating population size using capture-recapture methods, we estimated the number of MSM in Guatemala City and 95% CIs around this estimate, adjusted for RDS and TLS sampling design.ResultsA total of 2128 key chains were distributed in the first capture. Of the 501 MSM interviewed in the RDS survey, 200 (RDS adjusted, 23.4%) had received the key chain. Thus the RDS adjusted estimated population size of MSM in Guatemala City was 9,190 (95% CI 7765 to 10 616). Of the 504 MSM interviewed in the TLS survey, 193 (TLS adjusted, 32.1%) had received the key chain. The TLS adjusted estimated number of MSM was 6620 (95% CI 5813 to 7427).ConclusionsEstimates of MSM population size using the TLS survey resulted in a significantly lower estimate than that obtained through RDS survey, probably due to the fact that TLS targets MSM who attend venues. The estimate obtained through RDS may better reflect the size of the larger MSM population in Guatemala City, since this itRDS reaches MSM attending and not attending publicmeeting venues. Integrating capture-recapture methods in probability-based surveys among MSM is a simple and fast approach for providing the population sizes needed to inform and evaluate programs for MSM in Guatemala.
P1-S4.13 Mapping high risk activities of HIV/AIDS in Gaoxin and Yantan District of Zigong City
Authors: Zhang J , Yang Y , Zhou H , Yang C , Li Q , Song G , Xie Y , Blanchard J , Yu N , Ma X 
Published: July 2011

BackgroundZigong is located in the south of Sichuan Province of China. As a key area with a large number of migrants, Zigong has long been confronting the danger of HIV/AIDS. The goal of “Zigong geographic mapping on HIV/AIDS high-risk population” research project is to provide information on the location, type and volume of the female sex workers (FSWs) in Gaoxin (urban) and Yantan District (rural) to provide baseline information for HIV/AIDS prevention policy and programs in future.MethodsThis study adopted a “geographical approach” to map the location and spots of the activities of sex trade and estimated the number of FSWs involved in the activities. This included two sequential steps: 1) Systematic information gathering from key informants (KI) suggested the locations (“hot spots”) where FSWs congregate. 2) The “hot spots” were validated through site visit and insiders; the information about the number and characteristics of FSWs in each spot were collected.ResultsIn Gaoxin District: 59 high-risk spots were confirmed and 16 clusters were marked in 10 zones. The most common type of sex trade spots was hair salon/massage room/foot massage room. 72.9% of the spots were both “seeking risk” and “taking risk”, while 22.0% and 3.4% were only “seeking risk” and “taking risk” respectively. 39.0% of the spots had more than three clients per FSW per day. The estimated number of total FSWs in this urban area was 303. 38.5% of FSWs were in hotel/small lodge, while 29.3% and 27.3% were in small tea house/bar/KTV and hair salon/massage room/foot massage room respectively. The peak season, peak date and peak time of the most spots was summer, the whole week, afternoon and night. In Yantan District: 12 high-risk spots were confirmed and half were concentrated in Yantan Town. The most common type was small tea house/bar/KTV. Nine spots were both “seeking risk” and “taking risk”, while three were “taking risk” only. Five spots had more than three clients per day for each FSW. The estimated number of FSWs was 42, and 74.4% worked in the small tea house/bar/KTV. The peak season, peak date and peak time of the most spots was spring and summer, the whole week, and night, respectively.ConclusionsThe mapping approach provided direct and visible geographic distribution information, which enables a quick mastery of the distribution of high risk spots and the number of high risk population, for public health intervention planning and program implementation.
P1-S4.14 Does core theory apply in rural environments?
Authors: Gesink D , Sullivan A , Norwood T , Serre M , Miller W 
Published: July 2011

BackgroundThe expansion of core theory to include geographically defined core areas of elevated infection has been based primarily on spatial investigations into sexually transmitted infections (STIs) in large urban areas. It is uncertain whether core theory is applicable for rural environments. Our objective was to evaluate the concept of geographical core areas for gonorrhoea and syphilis in North Carolina, a rural state with urban pockets.MethodsWe analysed geomasked gonorrhoea and syphilis cases reported to the North Carolina State Health Department's sexually transmitted disease surveillance program from 1 January 2005 to 31 December 2007 for gonorrhoea and from 1 January 2000 to 31 December 2007 for syphilis. Incident gonorrhoea and syphilis rates were estimated using census tract level population estimates for the total North Carolina population from the US census. Rates were mapped by census tract and quarter. Rurality was measured at the census tract using two different definitions: percent rural and rural-urban commuting area (RUCA). RUCAs were used to classify North Carolina census tracts into rural, small town, micropolitan, or urban. SatScan was used to identify spatiotemporal clusters of significantly elevated rates of infection. Clusters were classified as outbreak or core based on duration. Clusters lasting the entire study period were considered potential core areas, while clusters of shorter duration were considered outbreak areas. Clusters were overlaid on maps of rurality and qualitatively assessed for correlation.ResultsOn average, gonorrhoea rates are low in the western mountains and higher in the eastern coastal part of the state. Most of the clusters were located in urban RUCAs or very low percent rural. Clusters for rural and small town RUCAs were of short duration and usually covered several census tracts and sometimes more than one county. Consequently, they were considered outbreak areas rather than core areas. Similar results were found for syphilis.ConclusionsWe found that core areas of elevated STIs were limited to the urban centers in rural environments. Significant clusters of infection in rural environments appear to be due to outbreaks. Rural environments may have core areas but not enough infection to sustain ongoing transmission. Bridge contacts may be more important for STI transmission in rural environments.
P1-S1.16 Estimating HIV incidence rate among stable sexual partnerships in sub-Saharan Africa
Authors: Chemaitelly H , Abu-Raddad L J 
Published: July 2011

BackgroundEmpirical evidence suggests that HIV incidence rate within stable discordant sexual partnerships in sub-Saharan Africa (SSA) varies between 1.2 and 19.0 per 100 person-years. Estimating HIV incidence rate within stable discordant partnerships is critical for determining the contribution of HIV sero-conversions among these partnerships to total HIV incidence.MethodsWe constructed a mathematical model based on competing-hazards formalism to estimate HIV incidence rate within stable discordant partnerships across 20 countries in SSA. We also used the model to analyse the patterns of HIV discordancy in SSA. The model was parameterised using Demographic Health Survey data and analyses were conducted at endemic equilibrium. Sensitivity analyses were performed to explore the dependence on the dynamical drivers of discordancy.ResultsOur model fitted well the empirical epidemiological measures of HIV discordancy and yielded an estimate for HIV incidence rate among discordant partnerships of 11.2 per 100 person-years (95% CI 8.9 to 13.4 per 100 person-years). HIV incidence rate ranged between 5.5 and 17.2 per 100 person-years across the countries. We also identified HIV incidence rate within stable discordant partnerships and HIV incidence rate from sources external to the partnership (or equivalently HIV prevalence) as key determinants of the variability in discordancy measures across SSA.ConclusionsOur estimate for the HIV incidence rate among discordant partnerships agrees well and falls in the mid-range of empirical estimates for this measure. There is however considerable variability across the countries. Biological and behavioural factors including differences in transmission rates such as due to male circumcision, may have contributed to the variability in HIV incidence rates among discordant partnerships across SSA. More research is needed to elucidate the determinants of this variability in incidence rates.
P1-S4.20 Mathematical modelling of HIV transmission and control among men who have sex with men: a review of 25 years of literature
Authors: Punyacharoensin N , Edmunds W J , De Angelis D , White R Guy 
Published: July 2011

BackgroundFor a quarter of century, mathematical models have been used to study the spread and control of HIV among men who have sex with men (MSM). We reviewed this literature to summarise the methodologies used, key model developments, and recommended strategies for HIV control among MSM.MethodsReview of the literature on dynamic compartmental models of HIV transmission among MSM was conducted. MEDLINE/EMBASE were searched from earliest date to end 2010.ResultsOf 742 studies identified, 127 studies met the inclusion criteria and were selected for review. Most studies employed deterministic methods (80%), and potentially as a result of this, as the complexity of models increased over time with respect to antiretroviral therapy (ART), there was a marked decline in the complexity of models with respect to sexual activity. Only a small proportion of models were fitted to data (22%) and even fewer were validated (17%), somewhat reducing confidence in the findings from these studies. That said, a number of common findings emerged, including (1) the importance of assumed changes in infectivity and sexual contact rates on the impact of ART on HIV incidence, and that this led to follow-up empirical studies to gather these data, and (2) the recommendation that multiple strategies would be required for effective HIV control among MSM.ConclusionsMathematical models have been useful in indentifying key empirical studies and for showing that multiple prevention strategies would be required for effective control of HIV epidemics in MSM. The lack of model fitting and validation emphasise that this area should be targeted for developments in the future. An improved methodology for parameter estimation will help generate predictions that more fully express uncertainty, allowing more informed public heath decision making.
P1-S4.23 Describing the progression fromChlamydia trachomatisto pelvic inflammatory disease: systematic review of mathematical models
Authors: Herzog S A , Heijne J C M , Althaus C L , Low N 
Published: July 2011

BackgroundChlamydia trachomatis(chlamydia) is an important cause of pelvic inflammatory disease (PID). Preventing PID is a main objective of chlamydia screening. There are many uncertainties about how and when bacteria spread from lower to upper genital tract. The potential impact of screening and treatment, which could interrupt ascending infection, might be affected by the timing of development of PID. Models are often used to investigate the potential impact of screening strategies on PID and should therefore include information about the timing of progression. We conducted a systematic review to determine how the progression from chlamydia to PID is described in mathematical models.MethodsWe searched four electronic databases using search terms related to mathematical models and PID from the earliest date to 19 October 2009 without language restrictions. Eligible publications included progression from chlamydia to PID either using a decision tree or a mathematical model. We extracted information about how authors conceptualised the dynamics of chlamydia infection and the development of PID, and assumptions about rates of progression.ResultsWe identified 41 unique publications about chlamydia infection; 28 of these included PID in a static decision tree. The average percentage of women developing PID in decision analyses was 22.9% (range 10–35%, n=26). For five publications it was not clear how the described model worked. The other eight publications described progression from chlamydia infection to PID dynamically. Of these, two models incorporated PID as a state in a Markov-chain model, four used compartmental models and two used individual-based models. Explicit statements about model structure included the possibility that PID can occur uniformly during a woman's infection, that tubal damage occurs in the second half of the chlamydia infection, and that the model had the ability to vary PID development time. Twenty-eight publications did not mention the stage during a chlamydia infection that progression to PID happens.ConclusionMost modelling studies do not consider dynamic aspects ofC trachomatistransmission and the timing of progression to PID. The mechanisms proposed in studies that made explicit statements could be compared to examine the impact of screening. We suggest that explicit statements about the timing and rates of progression would help improve understanding of the pathogenesis of chlamydial complications and the potential effects of screening.
P1-S4.24 Balancing the “supply and demand” of sex acts: implications for modelling the HIV epidemic among men who have sex with men in Southern India
Authors: Mitchell K , Foss A , Prudden H , Williams J , Johnson H , Pickles M , Phillips A , Ramesh B , Washington R , Vickerman P 
Published: July 2011

BackgroundIn India, men who have sex with men (MSM) have distinct identities related to the role taken in anal sex (Panthi/Bisexual (PB): mostly insertive, Kothi/Hijra (KH): mostly receptive, Double Deckers: both). Wide discrepancies are found between the supply and demand for sex acts estimated for each group using data on reported frequency of anal sex, role taken and estimated group population sizes.MethodsTwo methods for balancing the number and type of sex acts between different groups were compared. They were used in a deterministic HIV transmission model to estimate mixing patterns and HIV prevalence over the first 20 years of the epidemic (including reported condom use trends) and a subsequent 10-year intervention (10% absolute increase in condom use). Data collected from Bangalore for the evaluation of Avahan (the India AIDS initiative) on the mean reported frequency of sex acts per individual, role taken in anal sex and population sizes for each group were used to construct a mixing matrix. In method A, the PB group size was set to balance the total number of insertive and receptive acts, and receptive acts for each group were distributed among the three groups in proportion to the number of insertive acts offered. In method B, the proportion of receptive acts KH had with other KH was an additional input parameter, with remaining receptive acts distributed as in method A. The number and type of contacts for all groups were adjusted to achieve balancing. The model was run using 300 000 randomly sampled parameter sets drawn from the data and multiple fits were found to group-specific HIV prevalence data.ResultsModel fits for method B had more assortative (like-with-like) mixing than method A, particularly for PB (median number of acts PB have with other PB: 48.5% (IQR 33.3–63.3%) in A, 63.3% (IQR 47.3–74.1%) in B), related to larger PB group sizes and PB taking the insertive role less often in B. Despite these differences, the fitted epidemic curves were very similar for all three groups across the two methods (Absrtact P1-S4.24 figure 1), as was the predicted intervention impact (relative reduction in MSM HIV prevalence after 10 years: A: 18.2% (95% CI 11.0 to 29.2%), B: 18.1% (10.6 to 29.7%)).ConclusionsThe choice of method used to balance insertive and receptive contacts in an HIV transmission model affected the estimates for the amount of like-with-like mixing within different MSM groups, but the estimated impact of an intervention was robust to the method used.Abstract P1-S4.24 Figure 1MSM.
P1-S4.25 Using mathematical models to understand the causes of the ecological association seen between HIV and HSV-2 in female sex workers in Southern India
Authors: Mitchell K , Vickerman P , Pickles M , Kaushik M , Verma S , Isac S , Adhikary R , Mainkar M , Alary M , Boily M C 
Published: July 2011

BackgroundCross-sectional surveys of female sex workers (FSW) in multiple districts in Southern India show a strong ecological association between HIV and HSV-2 prevalence. Modelling was used to determine if this association is primarily due to shared behavioural risk factors (such as partner change rate) or if biological interactions between the two viruses also play a major role.MethodsLinear regression was used to find significant predictors of FSW HIV prevalence in 17 districts in Southern India (using data from Avahan, the India AIDS Initiative). Explanatory variables investigated included prevalence of different STIs in FSW and clients, mean duration of being an FSW or client, and mean reported number of clients per FSW or FSW visited per client. A deterministic HIV/HSV-2 transmission model without behavioural heterogeneity or transmission co-factors was parameterised using district-specific FSW and client behavioural data and fitted to HIV and HSV-2 prevalence data for each district by varying the per partnership HIV and HSV-2 transmission probabilities. The model was firstly fit to all districts simultaneously assuming a constant HIV and HSV-2 transmission probability to see whether district-level variations in behaviour were sufficient to explain the trends seen, and then fit separately for each district to test for trends in the estimated transmission parameters in different settings.ResultsFSW HSV-2, syphilis, gonorrhoea and chlamydia prevalence, client HIV prevalence and mean number of clients per FSW per week were all correlated with FSW HIV prevalence, but only FSW HSV-2 prevalence remained a significant predictor in multivariate analysis. The dynamic model reproduced the HIV/HSV-2 association when simultaneously fit to all districts, but was a poor fit to data (Abstract P1-S4.25 figure 1). When individual transmission probabilities were fit for each district positive correlations were seen between the HSV-2 transmission probability and both the HIV transmission probability and HSV-2 prevalence, but not between the HIV transmission probability and HSV-2 prevalence or vice versa.Abstract P1-S4.25 Figure 1FSW.ConclusionThese results suggest that differences in mean reported partner change rate or duration of commercial sex are not sufficient to explain the association between HIV and HSV-2 prevalence in FSW in Southern India. However, initial analyses do not show clear evidence for a biological interaction. More detailed models will be used to further investigate the association.
P1-S4.28 Survey of methodology used for the identification and antimicrobial susceptibility testing ofNeisseria gonorrhoeaein Latin America and the Caribbean
Authors: Starnino S , Liao M , Ruben M , Storey A , Dillon J A R ,   GASP-LAC Network
Published: July 2011

BackgroundThe Gonococcal Antimicrobial Susceptibility Surveillance Program in Latin America and the Caribbean (GASP-LAC) in the 1990s had significant impact in identifying trends in antimicrobial susceptibility in the region. To revitalise the GASP-LAC, a survey was undertaken to determine the level of surveillance activity and the methods used for the identification and antimicrobial susceptibility testing (AST) ofNeisseria gonorrhoeae(Ng) isolates.MethodsA structured questionnaire was distributed to potential participants to collect information regarding surveillance activities and methods used for identification and AST of Ng in LAC countries. Information was also obtained from presentations at the Workshop of the GASP-LAC in November 2010 in Buenos Aires, Argentina.Results7 countries completed the questionnaire and four provided unstructured answers regarding the methodologies. All 11 countries were interested in continuing to participate in the GASP-LAC. Of nine countries reporting, seven had an on-going country-wide network for gonococcal AST and two countries collected isolates locally, the number of isolates tested each year varied (25–400). Thayer Martin medium was used for Ng primary culture by all countries answering this question (n=8); among them, four countries used biochemical tests alone, or coupled with Gram stain (n=3) and one country, in addition to the two methods, used antigen detection and the nucleic acid amplification method. Chromogenic cephalosporin was used by all respondents (n=9) for detecting ß-lactamase production. Methods used for AST included agar dilution in 6 of 9 reporting countries, coupled with disc diffusion (n=4) and Etest (n=2); the remaining used disc diffusion alone (n=1) or coupled with Etest (n=2). CLSI interpretation criteria were used in all responding participants (n=9). Ng reference strains included ATCC49226 (n=6), coupled with WHO III, V, VII (n=2) or WHO A-E (n=1).ConclusionsDifferent levels of surveillance were noted between countries probably due to various resource availabilities. On the basis of these responses the GASP-LAC Co-ordinating Centre will re-establish and consolidate the GASP-LAC.