Weather Regulates Location, Timing, and Intensity of Dengue Virus Transmission between Humans and Mosquitoes

Background

Dengue is one of the most aggressively expanding mosquito-transmitted viruses. The human burden approaches 400 million infections annually. Complex transmission dynamics pose challenges for predicting location, timing, and magnitude of risk; thus, models are needed to guide prevention strategies and policy development locally and globally. Weather regulates transmission-potential via its effects on vector dynamics. An important gap in understanding risk and roadblock in model development is an empirical perspective clarifying how weather impacts transmission in diverse ecological settings. We sought to determine if location, timing, and potential-intensity of transmission are systematically defined by weather.

Methodology/Principal Findings

We developed a high-resolution empirical profile of the local weather-disease connection across Peru, a country with considerable ecological diversity. Applying 2-dimensional weather-space that pairs temperature versus humidity, we mapped local transmission-potential in weather-space by week during 1994-2012. A binary classification-tree was developed to test whether weather data could classify 1828 Peruvian districts as positive/negative for transmission and into ranks of transmission-potential with respect to observed disease. We show that transmission-potential is regulated by temperature-humidity coupling, enabling epidemics in a limited area of weather-space. Duration within a specific temperature range defines transmission-potential that is amplified exponentially in higher humidity. Dengue-positive districts were identified by mean temperature >22°C for 7+ weeks and minimum temperature >14°C for 33+ weeks annually with 95% sensitivity and specificity. In elevated-risk locations, seasonal peak-incidence occurred when mean temperature was 26-29°C, coincident with humidity at its local maximum; highest incidence when humidity >80%. We profile transmission-potential in weather-space for temperature-humidity ranging 0-38°C and 5-100% at 1°C x 2% resolution.

Conclusions/Significance

Local duration in limited areas of temperature-humidity weather-space identifies potential locations, timing, and magnitude of transmission. The weather-space profile of transmission-potential provides needed data that define a systematic and highly-sensitive weather-disease connection, demonstrating separate but coupled roles of temperature and humidity. New insights regarding natural regulation of human-mosquito transmission across diverse ecological settings advance our understanding of risk locally and globally for dengue and other mosquito-borne diseases and support advances in public health policy/operations, providing an evidence-base for modeling, predicting risk, and surveillance-prevention planning.

Timing and spatial-extent of diseases such as dengue and malaria that result from transmission between humans and mosquitoes are regulated by weather in complicated ways. For Aedes aegypti mosquitoes, the primary vector of dengue, slight changes in different components of weather have important effects on population dynamics, lifespan, biting-frequency, virus incubation period and capacity to transmit the virus, thus inducing changes in transmission probability. These complicated dynamics produce a weather-disease connection that is not well-defined for different ecological settings. Understanding this connection is important to critical elements of policy development and operational control of dengue such as predicting risk, developing human-vector transmission models, and planning surveillance-intervention strategies locally and globally. The empirical profile of the weather-disease connection for dengue developed in this study provides a needed understanding of how temperature and humidity work together in regulating human-mosquito transmission. The observed likelihood of low to epidemic-level transmission was highly sensitive to local seasonal duration in limited areas of this two-dimensional weather-space. Data presented represent a resource for estimating where and when transmission-potential supports epidemics of varying magnitude. This high-resolution weather-disease profile for dengue reveals systematic relationships that are informative for mosquito-borne diseases in general and discussions of consequences of global warming.

Clinical characteristics, drug resistance, and treatment outcomes among tuberculosis patients with diabetes in Peru

OBJECTIVES

Diabetes is a risk factor for active tuberculosis (TB). Data are limited regarding the association between diabetes and TB drug resistance and treatment outcomes. We examined characteristics of TB patients with and without diabetes in a Peruvian cohort at high risk for drug-resistant TB. Among TB patients with diabetes (TB-DM), we studied the association between diabetes clinical/management characteristics and TB drug resistance and treatment outcomes.

METHODS

During 2005-2008, adults with suspected TB with respiratory symptoms in Lima, Peru, who received rapid drug susceptibility testing (DST), were prospectively enrolled and followed during treatment. Bivariate and Kaplan-Meier analyses were used to examine the relationships of diabetes characteristics with drug-resistant TB and TB outcomes.

RESULTS

Of 1671 adult TB patients enrolled, 186 (11.1%) had diabetes. TB-DM patients were significantly more likely than TB patients without diabetes to be older, have had no previous TB treatment, and to have a body mass index (BMI) >18.5 kg/m(2) (p<0.05). In patients without and with previous TB treatment, the prevalence of multidrug-resistant TB was 23% and 26%, respectively, among patients without diabetes, and 12% and 28%, respectively, among TB-DM patients. Among 149 TB-DM patients with DST results, 104 (69.8%) had drug-susceptible TB and 45 (30.2%) had drug-resistant TB, of whom 29 had multidrug-resistant TB. There was no association between diabetes characteristics and drug-resistant TB. Of 136 TB-DM patients with outcome information, 107 (78.7%) had a favorable TB outcome; active diabetes management was associated with a favorable outcome.

CONCLUSIONS

Diabetes was common in a cohort of TB patients at high risk for drug-resistant TB. Despite prevalent multidrug-resistant TB among TB-DM patients, the majority had a favorable TB treatment outcome.

Impact of rapid drug susceptibility testing for tuberculosis: program experience in Lima, Peru

SETTING

Programmatic implementation of decentralized rapid drug susceptibility testing (DST) in Lima, Peru.

OBJECTIVE

Pre-post analysis compared time to diagnosis, treatment outcome and survival among patients tested with direct nitrate reductase assay (NRA) vs. indirect conventional methods.

DESIGN

From 2005 to 2009, we prospectively followed all patients referred for DST before (control) and after (intervention) NRA implementation. Among those referred for DST, NRA was used for smear-positive samples of patients with no prior history of multidrug resistance or treatment for multidrug-resistant tuberculosis (TB). Data were abstracted from patient charts and laboratory registers. Endpoints were favorable outcomes, time to result and time to death.

RESULTS

Of those patients who met the criteria for NRA, 740 underwent NRA and 621 underwent conventional DST. NRA yielded test results for 78.4% of cases vs. 68.8% for conventional DST (P < 0.0001); the median time to result was 44 vs. 133 days, respectively (adjusted HR 0.64, 95%CI 0.56-0.73). Among individuals without previous anti-tuberculosis treatment, NRA was associated with a favorable treatment outcome (adjusted OR 1.39, 95%CI 1.01-1.90) and prolonged survival (adjusted HR 0.53, 95%CI 0.31-0.90).

CONCLUSION

Direct NRA significantly shortened time to test result and improved treatment outcomes and survival in certain groups.

[Process of construction of the national research agenda on Human Resources in Health in Peru 2011 - 2014]

The National Health Authority of Peru, as part of the implementation of national priorities for health research in 2010 developed the process of building the national research agenda on health manpower (HM). In a scenario of technical challenges, national and international policy and under a nation-wide participatory approach with key stakeholders in the health system, training and aid HM linked to the subject, establishing a socially agreed agenda. Process consists of 3 phases: 1. National review of evidence and relevant information on RHUS, 2. Consultation with opinion leaders and subject experts, and 3. A collaborative space (national workshop) of deliberation, consensus and legitimacy of the agenda. Finally, we present the agenda consists of 30 research topics on health manpower, to be developed in the period 2011- 2014, and raises the challenges and prospects for implementation.

[Bibliometric analysis of scientific production about HIV/AIDS in Peru 1985-2010]

OBJECTIVE

To analyze the evolution of published scientific articles on HIV/AIDS in Peru.

METHODS

A bibliometric analysis of papers on HIV/AIDS published in journals indexed in MEDLINE, SciELO and LILACS until October 2010. We selected research papers fully developed in Peru, and multicenter studies with participating Peruvian sites.

RESULTS

We identified 257 publications on HIV/AIDS, showing an increase since 2003. The average publication delay was 2.8±1.8 years. Only 94 (36.6 %) articles were published in Spanish. The most studied areas were epidemiology (36.6 %) and clinical topics (35.8 %). The cross-sectional design was the most frequent (56.8 %) followed by case series. According to the WHO classification, studies to learn more about the disease and risk factors predominated (85.6 %) and according to the intervention areas, 46.7 % focused on diagnosis and treatment. Most studies were conducted in Lima (65.9 %). 48.2 % of studies focused on people living with HIV/AIDS. Finally, Revista Peruana de Medicina Experimental y Salud Pública was the journal that published most articles on HIV/AIDS (9.7 %).

CONCLUSIONS

We found a growth in scientific production on HIV/AIDS in Peru; however, we believe that the research undertaken was not based on an agreed national agenda or national research priorities, which might have limitted its dissemination and application.

[Management and funding of the research by the Peruvian National Institute of Health, 2004-2008]

The results of the research projects that have been approved and funded by the Instituto Nacional de Salud (Peru) during the period 2004-2008 were analyzed. Out of 182 approved and funded research projects, 150 (82%) were actually performed, 86% (129/150) ended in the final report and only 14% (18/129) were published in indexed journals, the mean time for publication of an article was of 2,7 years. Out of the presented research projects, 68 (45%) were through a competitive fund, 60 (40%) were institutional, 14 (9%) coming from regional (provincial) health directions and 8 (5%) collaborative. The executed budget was of $ 5,032,906.62. The mean amount assigned to each research project was $ 33,552.71 and the cost of each publication was $ 279,605.92; the distribution of the budget according to each study subject was 61% for communicable diseases, 12% for non-communicable diseases and 27% for technological development. The research promotion, development and financing in the Instituto Nacional de Salud during this period have had a decreasing trend, influenced by institutional policy. In order to overcome this situation, not only at an institutional but also at a national level, it is necessary that the State defines its national research policy, respecting the national and regional priorities in health research.

[Advances and challenges in building the national health research system in Peru]

The objective of this paper is to present the situational status of the National Health Research System of Peru (NHRS), the lessons learnt during the building process, the opportunities to improve it and the challenges. A description of the functions of the peruvian NHRS is done, in relation to governance, legal framework, research priorities, funding, creation and sustainability of resources and research production and utilization. It describes that in Peru we excert governance in research, we count with regulations, policy and research priorities, these last developed in the framework of a participatory, inclusive process. The conclusion reached is that the challenges of the peruvian NHRS are to consolidate the governance and to develop the mechanisms to articulate the stakeholders involved in research, to improve the resources allocation for research and innovation, to elaborate a plan for the development of human resources dedicated to research, to develop institutions and regional competences in order to perform research, and to link research in order to solve problems and make national research policies sustainable.

Programmatic implementation of rapid DST for Mycobacterium tuberculosis in Peru

BACKGROUND

Performance characteristics of novel rapid drug susceptibility tests (DST) for Mycobacterium tuberculosis may change when moving from research to implementation in actual public health practice. We describe the performance characteristics of a direct, rapid DST when implemented in Lima, Peru.

METHODS

A district laboratory validated conventional proportions and nitrate reductase methods. We collected data on samples submitted for DST from January 2005 to June 2007 and calculated frequency of testing and results, and median time to test results.

RESULTS

A total of 4102 DSTs were performed by conventional DST and 895 by nitrate reductase. Results were obtained from 72.8% of samples by conventional DST and from 70.2% of those processed by Griess; respectively 26.4% and 31.5% were multidrug-resistant tuberculosis. The median time from sample collection to test result was 31 days for Griess vs. 99 days for conventional DST.

CONCLUSIONS

Preliminary experience with the Griess method demonstrates favorable performance under program conditions.

Timely diagnosis of MDR-TB under program conditions: is rapid drug susceptibility testing sufficient?

Timely diagnosis and effective, safe treatment are essential to reduce transmission and improve outcomes for patients with tuberculosis. Aside from laboratory methods, many programmatic factors influence the overall turnaround time (TAT) in diagnosing multidrug-resistant tuberculosis (MDR-TB). We measured each step in the overall TAT required for MDR-TB in two of five health districts of Lima, Peru. The total TAT, from initial sputum specimen to diagnosis and appropriate treatment, was 5 months, almost twice as long as the bacteriological procedures per se. Expensive investments in laboratory technology may yield low returns unless the programmatic aspects of the diagnostic process are streamlined at the same time.