Microbiological diagnosis of prosthetic joint infections: a prospective evaluation of four bacterial culture media in the routine laboratory

The diagnosis of prosthetic joint infection (PJI) in the routine microbiology laboratory is labour-intensive, but semi-automated methods may be appropriate. We prospectively compared four microbiological culture methods on samples taken at prosthetic joint revision surgery. Automated BACTEC blood culture bottles and cooked meat enrichment broth were the most sensitive methods (87% and 83%, respectively, as compared with fastidious anaerobic broth (57%) and direct plates (39%)); all were highly specific (97–100%). To our knowledge, this is the first prospective study aimed at comparing culture methods in routine use in UK clinical laboratories for the diagnosis of PJI.     

Malaria

PURPOSE OF REVIEW: This review addresses recent developments that relate to the pathogenesis of severe malaria and its treatment, and also highlights the increase in the global burden of malaria and provides a summary of clinical trials of malaria vaccines. RECENT FINDINGS: Malaria, one of the world's most important parasitic infections, is on the increase globally. This has resulted in an increase in the morbidity and mortality from malaria in endemic areas, a resurgence in areas where it was previous eradicated, and an increase in imported malaria in Europe and North America. Mortality from severe malaria continues to be high, even when effective drugs are available, because most deaths occur within hours of admission to hospital. In severe malaria, the presence of acidosis is the most important prognostic factor in children and adults. A number of therapies have resulted in clinical improvements and the correction of acidosis in phase I and II studies, but larger trials are required to examine the effect on mortality. More malaria vaccines are now in phase I or II trials; however, available data do not yet promise an imminent impact on malaria control. SUMMARY: Recent developments include a better understanding of the pathogenesis of severe malaria, and have given rise to a number of novel therapeutic strategies that should be examined in larger phase III trials. Similarly, there has been considerable progress in the field of vaccine development.     

A phase 2b randomised trial of the candidate malaria vaccines FP9 ME-TRAP and MVA ME-TRAP among children in Kenya

Objective:     

Early gamma interferon and interleukin-2 responses to vaccination predict the late resting memory in malaria-naïve and malaria-exposed individuals

Two different cell populations respond to potent T-cell-inducing vaccinations. The induction and loss of effector cells can be seen using an ex vivo enzyme-linked immunospot (ELISPOT) assay, but the more durable resting memory response is demonstrable by a cultured ELISPOT assay. The relationship of the early effector response to durable resting memory is incompletely understood. Effector phenotype is usually identified by gamma interferon (IFN-gamma) production, but interleukin-2 (IL-2) has been specifically linked to the differentiation of memory cells. Here, IFN-gamma- and IL-2-secreting effector cells were identified by an ex vivo ELISPOT assay 1 week after vaccination and compared with the resting memory responses detected by a cultured ELISPOT assay 3 months later. The different kinetics and induction of IL-2 by different vaccines and natural exposure are described. Furthermore, both early IFN-gamma and IL-2 production independently predicted subsequent memory responses at 3 months in malaria-na?ve volunteers, but only IFN-gamma predicted memory in malaria-exposed volunteers. However, dual ELISPOT assays were also performed on malaria-exposed volunteers to identify cells producing both cytokines simultaneously. This demonstrated that double-cytokine-producing cells were highly predictive of memory. This assay may be useful in predicting vaccinations most likely to generate stable, long-term memory responses.     

Upregulation of TGF-beta, FOXP3, and CD4+CD25+ regulatory T cells correlates with more rapid parasite growth in human malaria infection

Understanding the regulation of immune responses is central for control of autoimmune and infectious disease. In murine models of autoimmunity and chronic inflammatory disease, potent regulatory T lymphocytes have recently been characterized. Despite an explosion of interest in these cells, their relevance to human disease has been uncertain. In a longitudinal study of malaria sporozoite infection via the natural route, we provide evidence that regulatory T cells have modifying effects on blood-stage infection in vivo in humans. Cells with the characteristics of regulatory T cells are rapidly induced following blood-stage infection and are associated with a burst of TGF-beta production, decreased proinflammatory cytokine production, and decreased antigen-specific immune responses. Both the production of TGF-beta and the presence of CD4+CD25+FOXP3+ regulatory T cells are associated with higher rates of parasite growth in vivo. P. falciparum-mediated induction of regulatory T cells may represent a parasite-specific virulence factor.     

Analysis of Immunity to Febrile Malaria in Children That Distinguishes Immunity from Lack of Exposure

In studies of immunity to malaria, the absence of febrile malaria is commonly considered evidence of “protection.” However, apparent “protection” may be due to a lack of exposure to infective mosquito bites or due to immunity. We studied a cohort that was given curative antimalarials before monitoring began and documented newly acquired asymptomatic parasitemia and febrile malaria episodes during 3 months of surveillance. With increasing age, there was a shift away from febrile malaria to acquiring asymptomatic parasitemia, with no change in the overall incidence of infection. Antibodies to the infected red cell surface were associated with acquiring asymptomatic infection rather than febrile malaria or remaining uninfected. Bed net use was associated with remaining uninfected rather than acquiring asymptomatic infection or febrile malaria. These observations suggest that most uninfected children were unexposed rather than “immune.” Had they been immune, we would have expected the proportion of uninfected children to rise with age and that the uninfected children would have been distinguished from children with febrile malaria by the protective antibody response. We show that removing the less exposed children from conventional analyses clarifies the effects of immunity, transmission intensity, bed nets, and age. Observational studies and vaccine trials will have increased power if they differentiate between unexposed and immune children.Malaria is a pressing global health problem (36). The correlates of immunity in observational field-based studies are often used to guide vaccine design (22), in which the chosen definition of immunity to malaria is usually the absence of febrile malaria. However, the findings obtained with this approach are often inconsistent, and responses to a specific antigen are associated with protection in some studies but not in others (4, 6, 7, 9-12, 23, 29). This may be because of parasite polymorphism (38), because of a confounding association between protective and nonprotective responses, because the endpoint of mild febrile malaria is not specific (26), or because rapidly waning antibody responses are not a stable predictive measure for the follow-up period (15).In studies in Kilifi, Kenya, associations between specific antibody responses and protection were stronger in children who had asymptomatic parasitemia at the start of monitoring (5, 16, 20, 28, 30, 31). This might imply that there is premunition, where a chronic low-level infection is required to provide immunity against further infection (35), and that antibody responses are more long lived in the presence of asymptomatic parasitemia (1). Alternatively, antibody responses measured in the presence of a challenge with asymptomatic parasitemia may be more informative than antibody responses measured without current exposure. For instance, protection against hepatitis B is predicted by the antibody titer shortly after vaccination, even when antibody titers subsequently become undetectable (32). However, it may simply be that parasitemia reflects greater exposure to malaria and hence a greater power to detect associations.In this study, we cleared asymptomatic parasitemia with highly effective antimalarials in order to identify newly acquired parasitemia during follow-up. We compared children who acquired asymptomatic parasitemia with children who developed febrile malaria by examining the associations with known markers of exposure and immunity. We then examined what impact excluding “unexposed” children had on conventional survival analyses in order to determine whether such analyses should be more widely used to study outcomes in observational studies or clinical trials.     

B cell memory to 3 Plasmodium falciparum blood-stage antigens in a malaria-endemic area

To gain insight into why antibody responses to malarial antigens tend to be short lived, we studied antigen-specific memory B cells from donors in an area where malaria is endemic. We compared antibody and memory B cell responses to tetanus toxoid with those to 3 Plasmodium falciparum candidate vaccine antigens: the C-terminal portion of merozoite surface protein 1 (MSP1(19)), apical membrane antigen 1 (AMA1), and the cysteine-rich interdomain region 1 alpha (CIDR1 alpha ) of a protein from the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family. These data are the first to be generated on memory B cells in children who are in the process of acquiring antimalarial immunity, and they reveal defects in B cell memory to P. falciparum antigens. Compared with the results for tetanus toxoid, more donors who were positive for antibody to AMA1 and CIDR1 alpha were negative for memory B cells. These data imply that some exposures to malaria do not result in the establishment of stable populations of circulating antigen-specific memory B cells, suggesting possible mechanisms for the short-lived nature of many anti-malarial antibody responses.