Adolescent Parental Monitoring Offers Protection Against Later Recurrent Driving After Drinking.

PURPOSE: Driving after drinking is a preventable threat to public health. We examined the prospective association of adolescent-reported parental monitoring knowledge (PMK) with recurrent driving after drinking in emerging adulthood. METHODS: We analyzed six annual rounds (1-4, 6, 11) of the National Longitudinal Survey of Youth 1997 with a sample of 5,261 participants. PMK variables were created to recategorize parental monitoring measures by age of the youth. Recurrent driving after drinking was measured in 2002 and 2007 and dichotomized. Unadjusted and adjusted binary logistic regressions analyzed the association of PMK at ages 14, 15, 16, and 17 with recurrent drinking after driving in 2002 (ages 18-23) and 2007 (ages 22-28). Adjusted models included age, sex, race, household income, and education. RESULTS: Mother's PMK from ages 14 to 17 was inversely associated with recurrent driving after drinking in 2002 (adjusted odds ratios [AORs]: 0.89 [p = .003, age 14], 0.93 [marginal p = .062, age 15], 0.88 [p = .0003, age 16], 0.88 [p = .0003, age 17]). By 2007, the only significant association between mother's PMK and recurrent driving after drinking was for age 16 (AOR: 0.95, p = .017). For father's PMK, significant inverse associations were only found for ages 16 and 17 with 2002 recurrent driving after drinking (AORs: 0.93, p = .025 and .88, p = .0005) and age 15 (AOR: 0.95, p = .021) with 2007 recurrent driving after drinking. DISCUSSION: Adolescent perceived PMK appears to offer protection against recurrent driving after drinking in emerging adulthood. This protective effect appears to wane as youth reach their mid-twenties.

Association of patient characteristics and insurance type with anti-obesity medications prescribing and fills.

AIM: To characterize factors associated with the receipt of anti-obesity medication (AOM) prescription and fill. MATERIALS AND METHODS: This retrospective cohort study used electronic health records from 1 January 2015 to 30 June 2023, in a large health system in Ohio and Florida. Adults with a body mass index ≥30 kg/m2 who attended ≥1 weight-management programme or had an initial AOM prescription between 1 July 2015 and 31 December 2022, were included. The main measures were a prescription for an AOM (naltrexone-bupropion, orlistat, phentermine-topiramate, liraglutide 3.0 mg and semaglutide 2.4 mg) and an AOM fill during the study follow-up. RESULTS: We identified 50 678 adults, with a mean body mass index of 38 ± 8 kg/m2 and follow-up of 4.7 ± 2.4 years. Only 8.0% of the cohort had AOM prescriptions and 4.4% had filled prescriptions. In the multivariable analyses, being a man, Black, Hispanic and other race/ethnicity (vs. White), Medicaid, traditional Medicare, Medicare Advantage, self-pay and other insurance types (vs. private insurance) and fourth quartile of the area deprivation index (vs. first quartile) were associated with lower odds of a new prescription. Hispanic ethnicity, being a man, Medicaid, traditional Medicare and Medicare Advantage insurance types, liraglutide and orlistat (vs. naltrexone-buproprion) were associated with lower odds of AOM fill, while phentermine-topiramate was associated with higher odds. Among privately insured individuals, the insurance carrier was associated with both the odds of AOM prescription and fill. CONCLUSIONS: Significant disparities exist in access to AOM both at the prescribing stage and getting the prescription filled based on patient characteristics and insurance type.

Early- and later-stage persistence with antiobesity medications: A retrospective cohort study.

OBJECTIVE: The study's objective was to examine the percentage of patients with an initial antiobesity medication (AOM) fill who were persistent with AOM at 3, 6, and 12 months and to characterize factors associated with persistence at 12 months. METHODS: This retrospective cohort study used electronic health records from January 2015 to July 2023 in a large health system in Ohio and Florida and included adults with BMI ≥30 kg/m2 who had an initial AOM prescription filled between 2015 and 2022. RESULTS: The authors identified 1911 patients with a median baseline BMI of 38 (IQR, 34-44). Over time, 44% were persistent with AOM at 3 months, 33% at 6 months, and 19% at 12 months. Across categories of AOM, the highest 1-year persistence was in patients receiving semaglutide (40%). Semaglutide (adjusted odds ratio [AOR] = 4.26, 95% CI: 3.04-6.05) was associated with higher odds of 1-year persistence, and naltrexone-bupropion (AOR = 0.68, 95% CI: 0.46-1.00) was associated with lower odds, compared with phentermine-topiramate. Among patients who were persistent at 6 months, a 1% increase in weight loss at 6 months was associated with 6% increased odds of persistence at year 1 (AOR = 1.06, 95% CI: 1.03-1.09). CONCLUSIONS: Later-stage persistence with AOM varies considerably based on the drug and the weight loss at 6 months.

Patient Portal Message Volume and Time Spent on the EHR: an Observational Study of Primary Care Clinicians.

BACKGROUND: As patient-initiated messaging rises, identifying variation in message volume and its relationship to clinician workload is essential. OBJECTIVE: To describe the association between variation in message volume over time and time spent on the electronic health record (EHR) outside of scheduled hours. DESIGN: Retrospective cohort study. PARTICIPANTS: Primary care clinicians at Cleveland Clinic Health System. MAIN MEASURES: We categorized clinicians according to their number of quarterly incoming medical advice messages (i.e., message volume) between January 2019 and December 2021 using group-based trajectory modeling. We assessed change in quarterly messages and outpatient visits between October-December 2019 (Q4) and October-December 2021 (Q12). The primary outcome was time outside of scheduled hours spent on the EHR. We used mixed effects logistic regression to describe the association between incoming portal messages and time spent on the EHR by clinician messaging group and at the clinician level. KEY RESULTS: Among the 150 clinicians, 31% were in the low-volume group (206 messages per quarter per clinician), 47% were in the moderate-volume group (505 messages), and 22% were in the high-volume group (840 messages). Mean quarterly messages increased from 340 to 695 (p < 0.001) between Q4 and Q12; mean quarterly outpatient visits fell from 711 to 575 (p = 0.005). While time spent on the EHR outside of scheduled hours increased modestly for all clinicians, this did not significantly differ by message group. Across all clinicians, each additional 10 messages was associated with an average of 12 min per quarter of additional time spent on the EHR (p < 0.001). CONCLUSIONS: Message volume increased substantially over the study period and varied by group. While messages were associated with additional time spent on the EHR outside of scheduled hours, there was no significant difference in time spent on the EHR between the high and low message volume groups.

Reducing antimicrobial overuse through targeted therapy for patients with community-acquired pneumonia: a study protocol for a cluster-randomized factorial controlled trial (CARE-CAP).

BACKGROUND: Community-acquired pneumonia (CAP) is a significant public health concern and a leading cause of hospitalization and inpatient antimicrobial use in the USA. However, determining the etiologic pathogen is challenging because traditional culture methods are slow and insensitive, leading to prolonged empiric therapy with extended-spectrum antibiotics (ESA) that contributes to increased hospital length of stay, and antimicrobial resistance. Two potential ways to reduce the exposure to ESA are (a) rapid diagnostic assays that can provide accurate results within hours, obviating the need for empiric therapy, and (b) de-escalation following negative bacterial cultures in clinically stable patients. METHODS: We will conduct a large pragmatic 2 × 2 factorial cluster-randomized controlled trial across 12 hospitals in the Cleveland Clinic Health System that will test these two approaches to reducing the use of ESA in adult patients (age ≥ 18 years) with CAP. We will enroll over 12,000 patients and evaluate the independent and combined effects of routine use of rapid diagnostic testing at admission and pharmacist-led de-escalation after 48 h for clinically stable patients with negative cultures vs usual care. We hypothesize that both approaches will reduce days on ESA. Our primary outcome is the duration of exposure to ESA therapy, a key driver of antimicrobial resistance. Secondary outcomes include detection of respiratory viruses, treatment with anti-viral medications, positive pneumococcal urinary antigen test, de-escalation by 72 h from admission, re-escalation to ESA after de-escalation, total duration of any antibiotic, 14-day in-hospital mortality, intensive care unit transfer after admission, healthcare-associated C. difficile infection, acute kidney injury, total inpatient cost, and hospital length-of-stay. DISCUSSION: Our study aims to determine whether identifying an etiological agent early and pharmacist-led de-escalation (calling attention to negative cultures) can safely reduce the use of ESA in patients with CAP. If successful, our findings should lead to better antimicrobial stewardship, as well as improved patient outcomes and reduced healthcare costs. Our findings may also inform clinical guidelines on the optimal management of CAP. TRIAL REGISTRATION: ClinicalTrials.gov NCT05568654 . Registered on October 4, 2022.

Monocyte pathology in human tuberculosis is due to plasma milieu changes and aberrant STAT signalling.

Monocyte-derived macrophages contribute centrally to immune protection in Mycobacterium tuberculosis infection and changes in monocyte phenotype characterize immunopathology in tuberculosis patients. Recent studies highlighted an important role of the plasma milieu in tuberculosis immunopathology. Here, we investigated monocyte pathology in patients with acute tuberculosis and determined tuberculosis plasma milieu effects on phenotype as well as cytokine signalling of reference monocytes. Patients with tuberculosis (n = 37) and asymptomatic contacts (controls n = 35) were recruited as part of a hospital-based study in the Ashanti region of Ghana. Multiplex flow cytometry phenotyping of monocyte immunopathology was performed and effects of individual blood plasma samples on reference monocytes prior to and during treatment were characterized. Concomitantly, cell signalling pathways were analysed to elucidate underlying mechanisms of plasma effects on monocytes. Multiplex flow cytometry visualization characterized changes in monocyte subpopulations and detected higher expression of CD40, CD64 and PD-L1 in monocytes from tuberculosis patients as compared to controls. Aberrant expression normalized during anti-mycobacterial treatment and also CD33 expression decreased markedly. Notably, higher CD33, CD40 and CD64 expression was induced in reference monocytes when cultured in the presence of plasma samples from tuberculosis patients as compared to controls. STAT signalling pathways were affected by the aberrant plasma milieu and higher levels of STAT3 and STAT5 phosphorylation was found in tuberculosis plasma-treated reference monocytes. Importantly, high pSTAT3 levels were associated with high CD33 expression and pSTAT5 correlated with CD40 as well as CD64 expression. These results suggested plasma milieu effects with potential implications on monocyte phenotype and function in acute tuberculosis.

Relationship Between Oral Temperature and Bacteremia in Hospitalized Patients.

BACKGROUND: Early recognition and treatment of bacteremia can be lifesaving. Fever is a well-known marker of bacteremia, but the predictive value of temperature has not been fully explored. OBJECTIVE: To describe temperature as a predictor of bacteremia and other infections. DESIGN: Retrospective review of electronic health record data. SETTING: A single healthcare system comprising 13 hospitals in the United States. PATIENTS: Adult medical patients admitted in 2017 or 2018 without malignancy or immunosuppression. MAIN MEASURES: Maximum temperature, bacteremia, influenza and skin and soft tissue (SSTI) infections based on blood cultures and ICD-10 coding. KEY RESULTS: Of 97,174 patients, 1,518 (1.6%) had bacteremia, 1,392 (1.4%) had influenza, and 3,280 (3.3%) had an SSTI. There was no identifiable temperature threshold that provided adequate sensitivity and specificity for bacteremia. Only 45% of patients with bacteremia had a maximum temperature ≥ 100.4˚F (38˚C). Temperature showed a U-shaped relationship with bacteremia with highest risk above 103˚F (39.4˚C). Positive likelihood ratios for influenza and SSTI also increased with temperature but showed a threshold effect at ≥ 101.0 ˚F (38.3˚C). The effect of temperature was similar but blunted for patients aged ≥ 65 years, who frequently lacked fever despite bacteremia. CONCLUSIONS: The majority of bacteremic patients had maximum temperatures below 100.4 ˚F (38.0˚C) and positive likelihood ratios for bacteremia increased with high temperatures above the traditional definition of fever. Efforts to predict bacteremia should incorporate temperature as a continuous variable.

Antibiotic perceptions, adherence, and disposal practices among parents of pediatric patients.

Antibiotics are frequently prescribed for children in the outpatient setting. Although sometimes necessary, antibiotic use is associated with important downstream effects including the development of antimicrobial resistance among human and environmental microorganisms. Current outpatient stewardship efforts focus on guiding appropriate antibiotic prescribing practices among providers, but little is known about parents' understanding of antibiotics and appropriate disposal of leftover antibiotics. To help bridge this gap, we conducted a qualitative study to assess parental understanding of their children's antibiotics, their adherence to antibiotic instructions, and their disposal practices. We conducted a semi-structured interview with parents of 13 children diagnosed with acute respiratory illnesses and prescribed antibiotics in an urban outpatient clinic. We found that parents had limited understanding of how antibiotics work. Although they received instructions about antibiotic use during the healthcare visit, adherence to the prescription and appropriate disposal of antibiotics was suboptimal. Limited baseline understanding of antibiotics, their prior experiences with antibiotics, perceptions about their social networks' antibiotic use, and information provided to them by healthcare providers may influence these behaviors. Our findings can inform educational efforts of outpatient stewardship programs to help optimize parental understanding of how to use and dispose of their children's antibiotics.

Longitudinal associations of emerging adults' drinking trajectories with their behavior, health, education and work outcomes 1, 4, and 9 years later.

BACKGROUND: To characterize emerging adults' drinking trajectories and their prospective association with later behavior, health, education, and work outcomes in later young adulthood. METHODS: This study used a selected cohort (N = 1622) from rounds 3-10 (aged 18-25), 11 (aged 26), 14 (aged 29), and 17 (aged 34) of the US National Longitudinal Survey of Youth 1997. Latent class growth modeling was used to identify trajectories of drinking (days ≥1 drink in the last 30 days) during emerging adulthood (aged 18-25) using data from rounds 3-10. Multinomial and linear regressions compared identified trajectory classes to outcomes measured 1, 4, and 9 years later. Covariates included sex, race, and urbanicity. RESULTS: Six drinking trajectories were identified: Abstainers (28.42%), Moderate Increasers (24.78%), Light Experimenters (11.96%), Heavy Experimenters (9.86%), Escalators (17.26%), and Heavy Users (7.71%). Compared to abstainers, emerging adults in other classes had significantly (p < .05 to.001) higher odds of binge drinking, smoking, and marijuana use at later rounds. Compared to abstainers, escalators had significantly higher education and income later. No significant difference in physical or mental health was found. CONCLUSION: Drinking behaviors formed during emerging adulthood continue into later lifetime periods in adulthood. The experimenters shifted their drinking behaviors to greater smoking and marijuana use, while heavy users supplemented their drinking behavior. Interventions in emerging adulthood (particularly ages 19-21), the period when individuals are becoming more independent but malleable, may mitigate adverse effects of alcohol overuse and improve later life behaviors and career outcomes.

Helicobacter pylori Management Is Associated with Predominantly Negative Patient Experiences: Results from a Focused Qualitative Analysis.

BACKGROUND: Helicobacter pylori eradication is associated with reduced gastric cancer and peptic ulcer disease incidence and mortality. Factors influencing patients' experiences surrounding H. pylori diagnosis and management are not well-described. Current patient perceptions can influence adherence to treatment, and also their anxieties related to this potentially carcinogenic condition. The objective of this study was to understand the patient experience surrounding H. pylori management and to qualitatively construct a contextual framework to inform and guide providers who manage patients with H. pylori infection. METHODS: We conducted a qualitative analysis using a focus group and one-on-one telephone interviews. An iterative inductive/deductive approach was applied to recorded transcripts to identify and hierarchically order themes. Patient experience was defined according to major themes within a structured health behavior framework. RESULTS: Theme saturation was achieved with thirteen participants (mean age 50.4 years; 62% female; 38% non-Hispanic white). Qualitative analysis yielded a total of 987 codes that resulted in five major themes related to the patient H. pylori experience: context of decision-making; health beliefs; barriers experienced; cues to action; and impact of new knowledge. These themes aligned with the Health Behavior Model framework. Participants were motivated to treat H. pylori. However, the experience was more often perceived negatively versus positively. The perceived patient-provider interaction contributed most prominently to the negative experience compared to other patient experiences, including treatment-related side effects. Internal cues, including symptoms and fear of cancer, modified participants' perceptions and motivation to accept treatment. CONCLUSIONS: Patient experiences related to H. pylori management are predominantly negative. Increasing providers' awareness about patients' values, beliefs, anxieties, and expectations surrounding H. pylori diagnosis/treatment may improve provider-patient communication and, ideally, related outcomes.

Opportunities and Challenges in Developing Technology-Based Social Skills Interventions for Adolescents with Autism Spectrum Disorder: A Qualitative Analysis of Parent Perspectives.

Interest continues to be high in technology-based interventions for individuals with autism spectrum disorder (ASD). Understanding the preferences and challenges of technology use among individuals with ASD can inform the design of such interventions. Through 18 interviews with parents, we used an iterative inductive-deductive approach to qualitative analysis and explored uses of technology for social skills development among adolescents with ASD. Our findings include parents' observations about their adolescent's preferences in types of technology devices and digital content, as well as both positive and negative effects of technology use on mood and behavior. Parents highlighted several avenues of technological preferences and risks that may inform intervention design, enhance user engagement, and capitalize on users' strengths while buttressing areas for growth.

Reproductive-Age Women's Experience of Accessing Treatment for Opioid Use Disorder: "We Don't Do That Here".

PURPOSE: For reproductive-age women, medications for opioid use disorder (OUD) decrease risk of overdose death and improve outcomes but are underutilized. Our objective was to provide a qualitative description of reproductive-age women's experiences of seeking an appointment for medications for OUD. METHODS: Trained female callers placed telephone calls to a representative sample of publicly listed opioid treatment clinics and buprenorphine providers in Florida, Kentucky, Massachusetts, Michigan, Missouri, North Carolina, Tennessee, Virginia, Washington, and West Virginia to obtain appointments to receive medication for OUD. Callers were randomly assigned to be pregnant or non-pregnant and have private or Medicaid-based insurance to assess differences in the experiences of access by these characteristics. The callers placed 28,651 uniquely randomized calls, 10,117 to buprenorphine-waivered prescribers and 754 to opioid treatment programs. Open-ended, qualitative data were obtained from the callers about the access experiences and were analyzed using a qualitative, iterative inductive-deductive approach. From all 28,651 total calls, there were 17,970 unique free-text comments to the question "Please give an objective play-by-play of the description of what happened in this conversation." FINDINGS: Analysis demonstrated a common path to obtaining an appointment. Callers frequently experienced long hold times, multiple transfers, and difficult interactions. Clinic receptionists were often mentioned as facilitating or obstructing access. Pregnant callers and those with Medicaid noted more barriers. Obtaining an appointment was commonly difficult even for these persistent, trained callers. CONCLUSIONS: Interventions are needed to improve the experiences of reproductive-age women as they enter care for OUD, especially for pregnant women and those with Medicaid coverage.

Staphylococcus aureus Resistance Patterns in Wisconsin: 2018 Surveillance of Wisconsin Organisms for Trends in Antimicrobial Resistance and Epidemiology (SWOTARE) Program Report.

OBJECTIVE: Surveillance of antimicrobial resistance patterns on a local level can reveal paradigms not obvious on a regional or national scale. Data collection from this perspective may potentially impact local prescribing patterns and empiric treatment guidelines. The objective of this study was to establish a baseline Staphylococcus aureus antibiogram for the state of Wisconsin and to elucidate potential geographic and demographic factors associated with antimicrobial resistance. DESIGN: Multi-center laboratory surveillance, with testing at a single site utilizing standardized media and susceptibility testing protocols. METHODS: 309 isolates of clinically-significant S. aureus were collected from hospital microbiology laboratories across Wisconsin in 2018, with distribution across seven geographic regions. Each isolate was tested using reference broth microdilution methods against a panel of 15 antimicrobial agents. Percentage susceptibility data, as well as median and 90th percentile minimum inhibitory concentration (MIC) values, were computed for each antimicrobial agent as a function of geographic region or demographic category. RESULTS: Increased resistance to penicillin (≥ 86.0% of isolates), erythromycin (≥ 56.8%), cefoxitin (≥ 45.5%), levofloxacin (≥ 25.0%), and clindamycin (≥ 20.5%) was observed in the Southcentral, Lake Winnebago, and Southeast regions of Wisconsin. In addition, isolates phenotypically classified as methicillin-resistant S. aureus (MRSA) were found to have increased rates of resistance to clindamycin, erythromycin, and levofloxacin as compared to S. aureus isolates susceptible to cefoxitin. S. aureus isolates demonstrated nearly 100% in vitro susceptibility to ceftaroline, dalbavancin, and telavancin. Statewide S. aureus isolates exhibited a vancomycin MIC90 of 1 µg/mL. S. aureus isolates from patients aged 20-39 years were more likely to demonstrate cefoxitin resistance when compared to other age groups (P ≤ 0.03), while isolates from patients ≥ 80 years were more likely to exhibit resistance to levofloxacin and clindamycin (P ≤ 0.046). CONCLUSIONS: Several antimicrobial agents continue to demonstrate in vitro efficacy against clinical isolates of S. aureus (including MRSA) throughout Wisconsin, including three agents with recently-published susceptibility testing guidelines. However, continued surveillance efforts may be necessary in the Lake Winnebago, Southeast, and Southcentral regions to further assess higher rates of resistance to a number of antimicrobial agents.

Experimental evolution with a multicellular host causes diversification within and between microbial parasite populations-Differences in emerging phenotypes of two different parasite strains.

Host-parasite coevolution is predicted to have complex evolutionary consequences, potentially leading to the emergence of genetic and phenotypic diversity for both antagonists. However, little is known about variation in phenotypic responses to coevolution between different parasite strains exposed to the same experimental conditions. We infected Caenorhabditis elegans with one of two strains of Bacillus thuringiensis and either allowed the host and the parasite to experimentally coevolve (coevolution treatment) or allowed only the parasite to adapt to the host (one-sided parasite adaptation). By isolating single parasite clones from evolved populations, we found phenotypic diversification of the ancestral strain into distinct clones, which varied in virulence toward ancestral hosts and competitive ability against other parasite genotypes. Parasite phenotypes differed remarkably not only between the two strains, but also between and within different replicate populations, indicating diversification of the clonal population caused by selection. This study highlights that the evolutionary selection pressure mediated by a multicellular host causes phenotypic diversification, but not necessarily with the same phenotypic outcome for different parasite strains.

Multiple-genotype infections and their complex effect on virulence.

Multiple infections are common. Although in recent years our understanding of multiple infections has increased significantly, it has also become clear that a diversity of aspects has to be considered to understand the interplay between co-infecting parasite genotypes of the same species and its implications for virulence and epidemiology, resulting in high complexity. Here, we review different interaction mechanisms described for multiple infections ranging from competition to cooperation. We also list factors influencing the interaction between co-infecting parasite genotypes and their influence on virulence. Finally, we emphasise the importance of between-host effects and their evolution for understanding multiple infections and their implications.

Host-Pathogen Coevolution: The Selective Advantage of Bacillus thuringiensis Virulence and Its Cry Toxin Genes.

Reciprocal coevolution between host and pathogen is widely seen as a major driver of evolution and biological innovation. Yet, to date, the underlying genetic mechanisms and associated trait functions that are unique to rapid coevolutionary change are generally unknown. We here combined experimental evolution of the bacterial biocontrol agent Bacillus thuringiensis and its nematode host Caenorhabditis elegans with large-scale phenotyping, whole genome analysis, and functional genetics to demonstrate the selective benefit of pathogen virulence and the underlying toxin genes during the adaptation process. We show that: (i) high virulence was specifically favoured during pathogen-host coevolution rather than pathogen one-sided adaptation to a nonchanging host or to an environment without host; (ii) the pathogen genotype BT-679 with known nematocidal toxin genes and high virulence specifically swept to fixation in all of the independent replicate populations under coevolution but only some under one-sided adaptation; (iii) high virulence in the BT-679-dominated populations correlated with elevated copy numbers of the plasmid containing the nematocidal toxin genes; (iv) loss of virulence in a toxin-plasmid lacking BT-679 isolate was reconstituted by genetic reintroduction or external addition of the toxins. We conclude that sustained coevolution is distinct from unidirectional selection in shaping the pathogen's genome and life history characteristics. To our knowledge, this study is the first to characterize the pathogen genes involved in coevolutionary adaptation in an animal host-pathogen interaction system.

Testing GxG interactions between coinfecting microbial parasite genotypes within hosts.

Host-parasite interactions represent one of the strongest selection pressures in nature. They are often governed by genotype-specific (GxG) interactions resulting in host genotypes that differ in resistance and parasite genotypes that differ in virulence depending on the antagonist's genotype. Another type of GxG interactions, which is often neglected but which certainly influences host-parasite interactions, are those between coinfecting parasite genotypes. Mechanistically, within-host parasite interactions may range from competition for limited host resources to cooperation for more efficient host exploitation. The exact type of interaction, i.e., whether competitive or cooperative, is known to affect life-history traits such as virulence. However, the latter has been shown for chosen genotype combinations only, not considering whether the specific genotype combination per se may influence the interaction (i.e., GxG interactions). Here, we want to test for the presence of GxG interactions between coinfections of the bacterium Bacillus thuringiensis infecting the nematode Caenorhabditis elegans by combining two non-pathogenic and five pathogenic strains in all possible ways. Furthermore, we evaluate whether the type of interaction, reflected by the direction of virulence change of multiple compared to single infections, is genotype-specific. Generally, we found no indication for GxG interactions between non-pathogenic and pathogenic bacterial strains, indicating that virulence of pathogenic strains is equally affected by both non-pathogenic strains. Specific genotype combinations, however, differ in the strength of virulence change, indicating that the interaction type between coinfecting parasite strains and thus the virulence mechanism is specific for different genotype combinations. Such interactions are expected to influence host-parasite interactions and to have strong implications for coevolution.

Sex differences in host defence interfere with parasite-mediated selection for outcrossing during host-parasite coevolution.

The Red Queen hypothesis proposes that coevolving parasites select for outcrossing in the host. Outcrossing relies on males, which often show lower immune investment due to, for example, sexual selection. Here, we demonstrate that such sex differences in immunity interfere with parasite-mediated selection for outcrossing. Two independent coevolution experiments with Caenorhabditis elegans and its microparasite Bacillus thuringiensis produced decreased yet stable frequencies of outcrossing male hosts. A subsequent systematic analysis verified that male C. elegans suffered from a direct selective disadvantage under parasite pressure (i.e. lower resistance, decreased sexual activity, increased escape behaviour), which can reduce outcrossing and thus male frequencies. At the same time, males offered an indirect selective benefit, because male-mediated outcrossing increased offspring resistance, thus favouring male persistence in the evolving populations. As sex differences in immunity are widespread, such interference of opposing selective constraints is likely of central importance during host adaptation to a coevolving parasite.

Increased responsiveness in feeding behaviour of Caenorhabditis elegans after experimental coevolution with its microparasite Bacillus thuringiensis.

Immune responses, either constitutive or induced, are costly. An alternative defence strategy may be based on behavioural responses. For example, avoidance behaviour reduces contact with pathogens and thus the risk of infection as well as the requirement of immune system activation. Similarly, if pathogens are taken up orally, preferential feeding of pathogen-free food may be advantageous. Behavioural defences have been found in many animals, including the nematode Caenorhabditis elegans. We here tested nematodes from a laboratory based evolution experiment which had either coevolved with their microparasite Bacillus thuringiensis (BT) or evolved under control conditions. After 48 generations, coevolved populations were more sensitive to food conditions: in comparison with the controls, they reduced feeding activity in the presence of pathogenic BT strains while at the same time increasing it in the presence of non-pathogenic strains. We conclude that host-parasite coevolution can drive changes in the behavioural responsiveness to bacterial microbes, potentially leading to an increased defence against pathogens.