Research news in brief

Cardiac surgery machines cause infection

University of Melbourne researchers have used genomics technology to show that a strain of a bacterium can be transmitted to patients from machines commonly used to regulate body temperature during cardiac surgery. Mycobacterium chimaera is a bacterial pathogen, which has previously been linked to the LivaNova Stockert 3T heating and cooling units used in hospitals in the northern hemisphere. The infection can cause serious illness; however, it may be treated with antibiotics. Three cases of the infection have been reported in Australia; two in NSW and one in Queensland. Researchers from the Peter Doherty Institute for Infection and Immunity have confirmed that the units are the source of the M. chimaera transmitted to patients. Published in the New England Journal of Medicine, the research analysed 48 M. chimaera samples obtained between May 2015 and July 2016, the majority from the heating and cooling units in question, and five from patients. “We think aerosols from the contaminated heater and cooler units drop into the sterile field during surgery and cause an infection,” Deputy Director of the Microbiological Diagnostic Unit Public Health Laboratory at the Doherty Institute, Dr Deborah Williamson said. “It’s a very hardy pathogen and, because it causes a latent infection, symptoms may not appear for months after surgery. We have uncovered this major public health problem using whole-genome sequencing technology and through national and international data sharing. In addition, we are developing a rapid diagnostic test for machine contamination and to detect M. chimaera infection in patients.”

Are “typically male” brains more prone to autism?

A German study has found that people whose brains are “typically male” are more likely to have autism spectrum disorder (ASD) than those whose brains are more “typically female”. ASD is a neurodevelopmental condition that is more common in males than females. The study, published in JAMA Psychiatry, examined the probability of ASD as a function of sex-related variation in brain anatomy, and included 98 right-handed, high-functioning adults with ASD and 98 neurotypical adults (aged 18–42 years) for comparison. Imaging and statistical analysis were used to assess ASD probability. The study based its analysis on cortical thickness in the brain because that can vary between males and females and be altered in people with ASD, according to the authors. The researchers reported that characteristically male anatomy of the brain was associated with a higher probability of risk for ASD than characteristically female brain anatomy. For example, biological females with more typical male brain anatomy were about three times more likely to have ASD than biological females with characteristically female brain anatomy, according to the study. The authors noted limitations of their findings, including the need for future research to examine possible causes. The study findings also must be replicated in other subgroups on the autism spectrum, they said. “Our study demonstrates that normative sex-related phenotypic diversity in brain structure affects the prevalence of ASD in addition to biological sex alone, with male neuroanatomical characteristics carrying a higher intrinsic risk for ASD than female characteristics,” the article concluded.

Managing drug-resistant tumours

When fighting drug-resistant infections or tumours, clinicians either use aggressive regimes in attempts to eliminate them completely, or they focus on containing the infection or tumour at tolerable levels. Deciding which course of action is appropriate is often difficult. A new mathematical analysis by American researchers, and published in PLOS Biology, has identified the factors that determine which of the two approaches will perform best, providing physicians and patients with new information to help them make difficult treatment decisions. Andrew Read, Professor from Penn State and an author of the study said: “We analysed when it might be better to use drugs to contain rather than try to eliminate the infection or tumour. We find that there are situations where containment would keep the patient alive longer, but also situations where it would make a dire situation even worse.” For the analysis, a patient was considered healthy and the infection or tumour was considered to be managed if it was maintained at or below a defined level of “acceptable burden”. Treatment failed if the pathogen load increased above this level. The analysis showed that the option leading to the longest time until treatment failure depended on the specific characteristics of the disease and of the patient being treated, but it provided a framework that doctors and patients could use to make more informed decisions about treatments. The researchers focused on two main factors that influence whether or not an infection or tumour will develop drug resistance. The first was the rate at which drug-sensitive cells become resistant. The second was “competitive suppression”, referring to the fact that the spread of drug-resistance can be slowed through competition for resources with drug-sensitive cells. Increased numbers of drug-responsive cells leads to more competition, preventing the spread of resistant cells, but it also means a greater risk of the sensitive cells developing resistance. “There are situations where we can be relatively sure that treatment will completely eliminate the infection or tumour, so aggressive treatment is the obvious choice” said Elsa Hansen, a research associate at Penn State and co-author of the article. “On the opposite end of the spectrum, there are low level situations, such as urinary-tract or ear infections, where a doctor may decide not to treat at all. The majority of cases, however, are somewhere in between and require hard choices that balance the damage caused by the infection or tumour and the risk of mutation with the damage caused by the treatment itself and the risk of developing uncontrollable resistance. Our analysis provides guidance for making these decisions from a standpoint of maximising patient wellbeing.”

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