Posts Tagged Public Health

Computers can predict effects of HIV policies, study suggests


ScienceDaily (July 27, 2012) — Policymakers in the fight against HIV/AIDS may have to wait years, even decades, to know whether strategic choices among possible interventions are effective. How can they make informed choices in an age of limited funding? A reliable, well-calibrated, predictive computer simulation would be a great help.

Policymakers struggling to stop the spread of HIV grapple with “what if” questions on the scale of millions of people and decades of time. They need a way to predict the impact of many potential interventions, alone or in combination. In two papers to be presented at the 2012 International AIDS Society Conference in Washington, D.C., Brandon Marshall, assistant professor of epidemiology at Brown University, will unveil a computer program calibrated to model accurately the spread of HIV in New York City over a decade and to make specific predictions about the future of the epidemic under various intervention scenarios.

“It reflects what’s seen in the real world,” said Marshall. “What we’re trying to do is identify the ideal combination of interventions to reduce HIV most dramatically in injection drug users.”

In an analysis that he’ll present on July 27, Marshall projects that with no change in New York City’s current programs, the infection rate among injection drug users will be 2.1 per 1,000 in 2040. Expanding HIV testing would drop the rate only 12 percent to 1.9 per 1,000; increasing drug treatment would reduce the rate 26 percent to 1.6 per 1,000; providing earlier delivery of antiretroviral therapy and better adherence would drop the rate 45 percent to 1.2 per 1,000; and expanding needle exchange programs would reduce the rate 34 percent to 1.4 per 1,000. Most importantly, doing all four of those things would cut the rate by more than 60 percent, to 0.8 per 1,000.

Virtual reality, real choices

The model is unique in that it creates a virtual reality of 150,000 “agents,” a programming term for simulated individuals, who in the case of the model, engage in drug use and sexual activity like real people.

Like characters in an all-too-serious video game, the agents behave in a world governed by biological rules, such as how often the virus can be transmitted through encounters such as unprotected gay sex or needle sharing.

With each run of the model, agents accumulate a detailed life history. For example, in one run, agent 89,425, who is male and has sex with men, could end up injecting drugs. He participates in needle exchanges, but according to the built-in probabilities, in year three he shares needles multiple times with another injection drug user with whom he is also having unprotected sex. In the last of those encounters, agent 89,425 becomes infected with HIV. In year four he starts participating in drug treatment and in year five he gets tested for HIV, starts antiretroviral treatment, and reduces the frequency with which he has unprotected sex. Because he always takes his HIV medications, he never transmits the virus further.

That level of individual detail allows for a detailed examination of transmission networks and how interventions affect them.

“With this model you can really look at the microconnections between people,” said Marshall, who began working on the model as a postdoctoral fellow at Columbia University and has continued to develop it since coming to Brown in January. “That’s something that we’re really excited about.”

To calibrate the model, Marshall and his colleagues found the best New York City data they could about how many people use drugs, what percentage of people were gay or lesbian, the probabilities of engaging in unprotected sex and needle sharing, viral transmission, access to treatment, treatment effectiveness, participation in drug treatment, progression from HIV infection to AIDS, and many more behavioral, social and medical factors. They also continuously calibrated it until the model could faithfully reproduce the infection rates among injection drug users that were known to occur in New York between 1992 and 2002.

And they don’t just run the simulation once. They run it thousands of times on a supercomputer at Brown to be sure the results they see are reliable.

Future applications

At Brown, Marshall is continuing to work on other aspects of the model, including an analysis of the cost effectiveness of each intervention and their combinations. Cost is, after all, another fact of life that policymakers and public health officials must weigh.

And then there’s the frustrating insight that the infection rate, even with four strengthened interventions underway, didn’t reduce the projected epidemic by much more than half.

“I actually expected something larger,” Marshall said. “That speaks to how hard we have to work to make sure that drug users can access and benefit from proven interventions to reduce the spread of HIV.”

Marshall’s collaborators on the model include Magdalena Paczkowski, Lars Seemann, Barbara Tempalski, Enrique Pouget, Sandro Galea, and Samuel Friedman.

The National Institutes of Health and the Lifespan/Tufts/Brown Center for AIDS Research provide financial support for the model’s continued development.

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The above story is reprinted from materials provided by Brown University.

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MRSA cases in academic hospitals double in five years


ScienceDaily (July 26, 2012) — Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) doubled at academic medical centers in the U.S. between 2003 and 2008, according to a report published in the August issue of Infection Control and Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America.

Researchers from the University of Chicago Medicine and the University HealthSystem Consortium (UHC) estimate hospitalizations increased from about 21 out of every 1,000 patients hospitalized in 2003 to about 42 out of every 1,000 in 2008, or almost 1 in 20 inpatients. “The rapid increase means that the number of people hospitalized with recorded MRSA infections exceeded the number hospitalized with AIDS and influenza combined in each of the last three years of the survey: 2006, 2007, and 2008,” said Michael David, MD, PhD, an assistant professor of medicine at the University of Chicago and one of the study’s authors.

The findings run counter to a recent CDC study that found MRSA cases in hospitals were declining. The CDC study looked only at cases of invasive MRSA — infections found in the blood, spinal fluid, or deep tissue. It excluded infections of the skin, which the UHC study includes.

MRSA infections, which cannot be treated with antibiotics related to penicillin, have become common since the late 1990s. These infections can affect any part of the body, including the skin, blood stream, joints, bones, and lungs.

The researchers attribute much of the overall increase they detected to community-associated infections — those that were contracted outside the healthcare setting. When MRSA first emerged it was primarily contracted in hospitals or nursing homes. “Community-associated MRSA infections, first described in 1998, have increased in prevalence greatly in the U.S. in the last decade,” David said. “Meanwhile, healthcare-associated strains have generally been declining.”

The study utilized the UHC database, which includes data from 90 percent of all not-for-profit academic medical centers in the U.S. However, like many such databases, the UHC data are based on billing codes hospitals submit to insurance companies, which often underestimate MRSA cases. For example, hospitals might not report MRSA cases that do not affect insurance reimbursement for that particular patient. In other cases, hospitals might be limited in the number of billing codes they can submit for each patient, which can result in a MRSA code being left off the billing report if it was not among the primary diagnoses.

David and his team corrected for these errors by using detailed patient observations from the University of Chicago Medical Center and three other hospitals. They looked at patient records to find the actual number of MRSA cases in each hospital over a three-year period. The team then checked the insurance billing data to see how many of those cases were actually recorded. They found that the billing data missed one-third to one-half of actual MRSA cases at the four hospitals. They used that rate of error as a proxy to correct the billing data from other 420 hospitals in the UHC database and arrive at the final estimates.

“I think this is still an underestimate of actual cases,” David said. “But we can say with some assurance that this correction gives us a more accurate lower bound for how many cases [of MRSA] there actually are. What’s clear from our data is that cases were on the rise in academic hospitals in 2003 to 2008.”

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The above story is reprinted from materials provided by University of Chicago Press Journals, via EurekAlert!, a service of AAAS.

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Journal Reference:

  1. Michael Z. David, Sofia Medvedev, Samuel F. Hohmann, Bernard Ewigman, Robert S. Daum. Increasing Burden of Methicillin-Resistant Staphylococcus aureus Hospitalizations at US Academic Medical Centers, 2003? Infection Control and Hospital Epidemiology, August 2012 [link]

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Ecstasy harms memory with one year of recreational use


ScienceDaily (July 25, 2012) — There has been significant debate in policy circles about whether governments have over-reacted to ecstasy by issuing warnings against its use and making it illegal. In the UK, David Nutt said ecstasy was less dangerous than horseback riding, which led to him being fired as the government’s chief drug advisor. Others have argued that ecstasy is dangerous if you use it a lot, but brief use is safe.

New research published online July 25 by the scientific journal Addiction, gives some of the first information available on the actual risk of using ecstasy. It shows that even in recreational amounts over a relatively short time period, ecstasy users risk specific memory impairments. Further, as the nature of the impairments may not be immediately obvious to the user, it is possible people wouldn’t get the signs that they are being damaged by drug use until it is too late.

According to the study, new ecstasy users who took ten or more ecstasy pills over their first year of use showed decreased function of their immediate and short-term memory compared with their pre-ecstasy performance. These findings are associated with damage of the hippocampus, the area of the brain that oversees memory function and navigation. Interestingly, hippocampal damage is one of the first signs of Alzheimer’s disease, resulting in memory loss and disorientation.

The study participants took an average of 32 pills each over the course of the year, or about two and a half pills per month. Some participants took as few as ten pills over the year and still showed signs of memory impairments.

Lead author Dr. Daniel Wagner says: “This study was designed to minimize the methodological limitations of earlier research, in which it was not possible to say whether cognitive impairments seen among ecstasy users were in place before drug use began. By measuring the cognitive function of people with no history of ecstasy use and, one year later, identifying those who had used ecstasy at least ten times and remeasuring their performance, we have been able to start isolating the precise cognitive effects of this drug.”

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