RESUMO
SUMMARYThe weekly number of dengue cases in Peru, South America, stratified by province for the period 1994-2006 were analysed in conjunction with associated demographic, geographic and climatological data. Estimates of the reproduction number, moderately correlated with population size (Spearman rho=0.28, P=0.03), had a median of 1.76 (IQR 0.83-4.46). The distributions of dengue attack rates and epidemic durations follow power-law (Pareto) distributions (coefficient of determination >85%, P<0.004). Spatial heterogeneity of attack rates was highest in coastal areas followed by mountain and jungle areas. Our findings suggest a hierarchy of transmission events during the large 2000-2001 epidemic from large to small population areas when serotypes DEN-3 and DEN-4 were first identified (Spearman rho=-0.43, P=0.03). The need for spatial and temporal dengue epidemic data with a high degree of resolution not only increases our understanding of the dynamics of dengue but will also generate new hypotheses and provide a platform for testing innovative control policies.
Assuntos
Vírus da Dengue/fisiologia , Dengue/epidemiologia , Surtos de Doenças , Clima , Dengue/transmissão , Geografia , Incidência , Peru/epidemiologia , Densidade Demográfica , Análise de Regressão , Fatores de TempoRESUMO
Dengue, a vector-borne disease, thrives in tropical and subtropical regions worldwide. A retrospective analysis of the 2002 dengue epidemic in Colima located on the Mexican central Pacific coast is carried out. We estimate the reproduction number from spatial epidemic data at the level of municipalities using two different methods: (1) Using a standard dengue epidemic model and assuming pure exponential initial epidemic growth and (2) Fitting a more realistic epidemic model to the initial phase of the dengue epidemic curve. Using Method I, we estimate an overall mean reproduction number of 3.09 (95% CI: 2.34,3.84) as well as local reproduction numbers whose values range from 1.24 (1.15,1.33) to 4.22 (2.90,5.54). Using Method II, the overall mean reproduction number is estimated to be 2.0 (1.75,2.23) and local reproduction numbers ranging from 0.49 (0.0,1.0) to 3.30 (1.63,4.97). Method I systematically overestimates the reproduction number relative to the refined Method II, and hence it would overestimate the intensity of interventions required for containment. Moreover, optimal intervention with defined resources demands different levels of locally tailored mitigation. Local epidemic peaks occur between the 24th and 35th week of the year, and correlate positively with the final local epidemic sizes (rho=0.92, P-value<0.001). Moreover, final local epidemic sizes are found to be linearly related to the local population size (P-value<0.001). This observation supports a roughly constant number of female mosquitoes per person across urban and rural regions.
Assuntos
Dengue/epidemiologia , Surtos de Doenças/estatística & dados numéricos , Humanos , Matemática , México/epidemiologia , Modelos Estatísticos , Estudos RetrospectivosRESUMO
We model an outbreak of acute haemorrhagic conjunctivitis (AHC) using a simple epidemic model that includes susceptible, infectious, reported, and recovered classes. The model's framework considers the impact of underreporting and behaviour changes on the transmission rate and is applied to a recent epidemic of AHC in Mexico, using a fit to the cumulative number of cases to estimate model parameters, which agree with those derived from clinical studies. The model predicts a 'mean time from symptomatic onset to diagnosis' of 1.43 days (95 per cent CI: 1-2.5) and that the final size of the Mexican epidemic was underreported by 39 per cent. We estimate that a primary infectious case generates approximately 3 secondary cases (R0* = 2.64, SD 0.65). We explore the impact of interventions on the final epidemic size, and estimate a 36 per cent reduction in the transmission rate due to behaviour changes. The effectiveness of the behaviour changes in slowing the epidemic is evident at 21.90 (SD 0.19) days after the first reported case. Results therefore support current public health policy including expeditious announcement of the outbreak and public health information press releases that instruct individuals on avoiding contagion and encourage them to seek diagnosis in hospital clinics.
Assuntos
Infecções por Adenoviridae/transmissão , Adenoviridae/crescimento & desenvolvimento , Conjuntivite Hemorrágica Aguda/transmissão , Surtos de Doenças , Modelos Biológicos , Modelos Estatísticos , Infecções por Adenoviridae/epidemiologia , Infecções por Adenoviridae/virologia , Terapia Comportamental , Conjuntivite Hemorrágica Aguda/epidemiologia , Conjuntivite Hemorrágica Aguda/virologia , Notificação de Doenças , Humanos , México/epidemiologia , Saúde Pública/métodos , Clima TropicalRESUMO
A model of epidemic dispersal (based on the assumption that susceptible cattle were homogeneously mixed over space, or non-spatial model) was compared to a partially spatially explicit and discrete model (the spatial model), which was composed of differential equations and used geo-coded data (Euclidean distances between county centroids). While the spatial model accounted for intra- and inter-county epidemic spread, the non-spatial model did not assess regional differences. A geo-coded dataset that resembled conditions favouring homogeneous mixing assumptions (based on the 2001 Uruguayan foot-and-mouth disease epidemic), was used for testing. Significant differences between models were observed in the average transmission rate between farms, both before and after a control policy (animal movement ban) was imposed. They also differed in terms of daily number of infected farms: the non-spatial model revealed a single epidemic peak (at, approximately, 25 epidemic days); while the spatial model revealed two epidemic peaks (at, approximately, 12 and 28 days, respectively). While the spatial model fitted well with the observed cumulative number of infected farms, the non-spatial model did not (P<0.01). In addition, the spatial model: (a) indicated an early intra-county reproductive number R of approximately 87 (falling to <1 within 25 days), and an inter-county R<1; (b) predicted that, if animal movement restrictions had begun 3 days before/after the estimated initiation of such policy, cases would have decreased/increased by 23 or 26%, respectively. Spatial factors (such as inter-farm distance and coverage of vaccination campaigns, absent in non-spatial models) may explain why partially explicit spatial models describe epidemic spread more accurately than non-spatial models even at early epidemic phases. Integration of geo-coded data into mathematical models is recommended.
Assuntos
Transmissão de Doença Infecciosa/veterinária , Febre Aftosa/epidemiologia , Febre Aftosa/transmissão , Animais , Bovinos , Reprodutibilidade dos Testes , Ovinos , Conglomerados Espaço-Temporais , Suínos , Uruguai/epidemiologiaRESUMO
Scorpionism is an endemic public health problem in Mexico [Hoffmann, C.C., 1936. La distribucion geografica de los alacranes peligrosos en la Republica Mexicana. Bol. Inst. Hygiene Mex. 2, 321; Hoffmann, C.C., Nieto, D.R., 1939. Segunda contribucion al conocimiento de los alacranes mexicanos. Anal. Inst. Biol. 10, 83-92; Mazzoti, L., Bravo-Becherelle, M.A., 1963. Scorpionism in the Mexican Republic. In: Keegan, H.L., McFarlane, W.V. (Eds.), Venomous and Poissonous Animals and Noxious Plants of the Pacific Area. Pergamon Press, London, pp. 119-131; Monroy-Velasco, J., 1961. Alacranes venenosos de Mexico. Rev. Mex. Cien. Med. Biol., Mex. 1, 1-23; Diaz-Najera, A., 1975. Listas y datos de distribucion geografica de los alacranes de Mexico. Rev. Inv. Salud. Publica. (Mex.) 35, 1; Velasco-Castrejon, O., Lara-Aguilera, R., Alatorre, H., 1976. Aspectos epidemiologicos y clinicos de la picadura de alacran en una area hiperendemica. Rev. Inv. Salud Publica. (Mex.) 36, 93-103; Dehesa-Davila, M., Possani, L.D., 1994. Scorpionism and serotherapy in Mexico. Toxicon 32 (9), 1015-1018]. In this prospective study, we assess cardiovascular disorders in children via electrocardiographic (ECG) recordings following envenomation by scorpion species Centruroides limpidus tecomanus found in the state of Colima, Mexico. We analyzed 113 cases between the ages of 5 and 14 years. Among the most frequent symptoms presented included local pain (99.1%) and paresthesia (75.2%), pruritus (36.3%), sialorrhoea (35.4%), and nystagmus (24.8%). Cardiovascular disorders were observed in 39.8% of cases, 71% of which were rhythm abnormalities. We find a significant association between the frequency of ECG alterations and age, whereby 8-9-year-old children are more likely to experience ECG alterations when compared with other tested age groups.
Assuntos
Arritmias Cardíacas/etiologia , Picadas de Escorpião/fisiopatologia , Adolescente , Fatores Etários , Animais , Antivenenos/uso terapêutico , Criança , Pré-Escolar , Eletrocardiografia , Feminino , Humanos , Masculino , Estudos Prospectivos , Picadas de Escorpião/tratamento farmacológico , EscorpiõesRESUMO
The time available to implement successful control measures against epidemics was estimated. Critical response time (CRT), defined as the time interval within which the number of epidemic cases remains stationary (so that interventions implemented within CRT may be the most effective or least costly), was assessed during the early epidemic phase, when the number of cases grows linearly over time. The CRT was calculated from data of the 2001 foot-and-mouth disease (FMD) epidemic that occurred in Uruguay. Significant regional CRT differences (ranging from 1.4 to 2.7 days) were observed. The CRT may facilitate selection of control measures. For instance, a CRT equal to 3 days would support the selection of measures, such as stamping-out, implementable within 3 days, but rule out measures, such as post-outbreak vaccination, because intervention and immunity building require more than 3 days. Its use in rapidly disseminating diseases, such as FMD, may result in regionalized decision-making.
Assuntos
Animais Domésticos , Surtos de Doenças/veterinária , Febre Aftosa/epidemiologia , Febre Aftosa/prevenção & controle , Animais , Tomada de Decisões , Árvores de Decisões , Surtos de Doenças/prevenção & controle , Febre Aftosa/transmissão , Modelos Biológicos , Fatores de Risco , Fatores de Tempo , Uruguai/epidemiologia , Vacinação/veterináriaRESUMO
En este artículo hemos introducido, por primera vez, un modelo matemático para el estudio de la dinámica de enfermedades transmisibles, que toma en consideración el impacto de transmisión en dos ambientes diferentes para una población heterogénea. Calculamos el número reproductivo básico y determinamos el impacto de homotransmisiones y heterotransmisiones en el número de infecciones secundarias
Assuntos
Doenças Transmissíveis , Computação Matemática , Dinâmica Populacional , Meios de Transporte , Tuberculose Pulmonar , Pesquisa Ambiental , PesquisaRESUMO
En este artículo hemos introducido, por primera vez, un modelo matemático para el estudio de la dinámica de enfermedades transmisibles, que toma en consideración el impacto de transmisión en dos ambientes diferentes para una población heterogénea. Calculamos el número reproductivo básico y determinamos el impacto de homotransmisiones y heterotransmisiones en el número de infecciones secundarias
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Tuberculose Pulmonar/epidemiologia , Computação Matemática , Dinâmica Populacional , Doenças Transmissíveis , Meios de Transporte , Pesquisa , Pesquisa AmbientalRESUMO
Tuberculosis (TB) transmission is enhanced by systematic exposure to an infectious individual. This enhancement usually takes place at either the home, workplace, and/or school (generalized household). Typical epidemiological models do not incorporate the impact of generalized households on the study of disease dynamics. Models that incorporate cluster (generalized household) effects and focus on their impact on TB's transmission dynamics are developed. Detailed models that consider the effect of casual infections, that is, those generated outside a cluster, are also presented. We find expressions for the Basic Reproductive Number as a function of cluster size. The formula for R0 separates the contributions of cluster and casual infections in the generation of secondary TB infections. Relationships between cluster and classical epidemic models are discussed as well as the concept of critical cluster size.
Assuntos
Análise por Conglomerados , Modelos Estatísticos , Tuberculose/transmissão , Causalidade , Humanos , Incidência , PrevalênciaRESUMO
In this paper a regenerative argument is used to derive an expression for the expectation of the integral under the stochastic path of a birth-death Markov process up to extinction time as well as for the expected time to extinction. Some applications to classical-birth-death processes are given.