A Risk-based Model for Predicting the Impact of using Condoms on the Spread of Sexually Transmitted Infections.

We create and analyze a mathematical model to estimate the impact of condom-use and sexual behavior on the prevalence and spread of Sexually Transmitted Infections (STIs). STIs remain a significant public health challenge globally with a high burden of some Sexually Transmitted Diseases (STDs) in both developed and undeveloped countries. Although condom-use is known to reduce the transmission of STIs, there are a few quantitated population-based studies on the protective role of condom-use in reducing the incidence of STIs. The number of concurrent partners is correlated with their risk of being infectious by a STI such as chlamydia, gonorrhea, or syphilis. We define a Susceptible-Infectious-Susceptible (SIS) model that distributes the population by the number of concurrent partners. The model captures the multi-level heterogeneous mixing through a combination of biased (preferential) and random mixing between individuals with different risks, and accounts for differences in condom-use in the low- and high-risk populations. We use sensitivity analysis to assess the relative impact of high-risk people using condom as a prophylactic to reduce their chance of being infectious, or infecting others. The model predicts the STI prevalence as a function of the number of partners that a person has, and quantifies how this distribution changes as a function of condom-use. Our results show that when the mixing is random, then increasing the condom-use in the high-risk population is more effective in reducing the prevalence than when many of the partners of high-risk people have high risk. The model quantified how the risk of being infected increases for people who have more partners, and and the need for high-risk people to consistently use condoms to reduce their risk of infection.

Clinical diagnosis delays and epidemiology of dengue fever during the 2002 outbreak in Colima, Mexico.

Dengue fever is a re-emergent and challenging public health problem in the world. Here, we assess retrospectively the epidemiological and clinical characteristics of the 2002 dengue epidemic in the state of Colima, Mexico. This study is carried out by analysing a database containing demographic, epidemiological and clinical information. Of the 4040 clinical dengue cases diagnosed in the hospitals of the Mexican Institute of Public Health in the state of Colima, 548 cases were confirmed by laboratory tests, and 495 cases presented at least one haemorrhagic manifestation. Of the total clinically diagnosed cases, the most common symptoms observed were: fever (99.6%), headache (92.4%), myalgia (89.4%) and arthralgia (88.6%). The most common haemorrhagic manifestations were: petechiae (7.1%), gingivitis (3.4%) and epistaxis (3.6%). The median time between the onset of illness and visit to the health care clinic (diagnostic delay) was 1 day (interquartile range [IQR]: 0-3). For cases presenting haemorrhagic manifestations, the diagnostic delay was higher (median: 2 days, IQR: 0-4) than for non-haemorrhagic cases (median: 1 day, IQR: 0-3). The proportion of males presenting haemorrhagic manifestations was higher than females (Fisher Exact test; p