Hepatitis C in the pediatric population: Transmission, natural history, treatment and liver transplantation

Pediatric Liver Transplant Pathology: An Update and Practical Consideration

This review provides a summary of the diagnostic approach to pediatric liver transplantation (LT) pathology. It emphasizes the pathologic features of T-cell-mediated rejection, the most common finding on liver allograft biopsies, and discusses other forms of rejection, including the less frequent antibody-mediated rejection. The article incorporates insights from the recently published Banff 2022 Liver Group Meeting Report. Additionally, it covers other complications such as biliary and vascular issues, infections, and disease recurrence. Finally, the review summarizes the potential applications of novel technologies, including next-generation pathology and artificial intelligence, in the context of pediatric LT pathology.

Cost-utility Analysis of Second-generation Direct-acting Antivirals for Hepatitis C

Background: Hepatitis C virus (HCV) can lead to increased mortality, disability, and liver transplantation if left untreated, and it is associated with a possible increase in disease burden in the future, all of which would surely have a significant impact on the health system. New antiviral regimens are effective in the treatment of the disease yet expensive. Objectives: The purpose of the present study was to assess the cost-effectiveness of three medication regimens, namely, ledipasvir/sofosbuvir (LDV/SOF), velpatasvir/sofosbuvir, and daclatasvir/sofosbuvir (DCV/SOF) for HCV patients with genotype 1 in Iran. Methods: A Markov model with a lifetime horizon was developed to predict the costs and outcomes of the three mentioned medication therapy strategies. The final outcome of the study was quality-adjusted life-years (QALYs), which was obtained using the previously published studies. The study was conducted from the perspective of the Health Ministry; therefore, only direct medical costs were estimated. The results were provided as the incremental cost-effectiveness ratio (ICER) per QALY. Ultimately, the one-way and probabilistic sensitivity analyses were used to measure the strength of study results. Results: The results showed that the QALYs for LDV/SOF, DCV/SOF, and VEL/SOF were 13.25, 13.94, and 14.61, and the costs were 4,807, 7,716, and 4,546$, respectively. The VEL/SOF regimen had lower costs and higher effectiveness than the LDV/SOF and DCV/SOF regimens, making it a dominant strategy. The tornado diagram results showed that the study results had the highest sensitivity to chronic hepatitis C (CHC) and compensated cirrhosis (CC) state costs. Moreover, the scatter plots showed that the VEL/SOF was the dominant therapeutic strategy in 73% of the simulations compared to LDV/SOF and 66% of the simulations compared to DCV/SOF; moreover, it was in the acceptable region in 92% of the simulations and below the threshold. Therefore, it was considered the most cost-effective strategy. Moreover, the results showed that DCV/SOF was in the acceptable region below the threshold in 69% of the simulations compared to LDV/SOF. Therefore, the DCV/SOF regimen was more cost-effective than LDV/SOF. Conclusions: According to the present study results, it is suggested that the VEL/SOF regimen be used as the first line of therapy in patients with HCV genotype 1. Moreover, DCV/SOF can be the second-line medication regimen.

The Changing Epidemiology of Liver Disease Among US Children and Adolescents From 1999 to 2016

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) and infection with hepatitis B virus (HBV) or hepatitis C virus (HCV) are major causes of liver disease in adults. However, data for children and adolescents are limited. Our study aimed to characterize the prevalence, trend, and risk factors of infection of HBV and HCV and possible NAFLD for this population.

METHODS

We analyzed 6,647 children and adolescents (aged 6-21 years) from the 1999-2016 National Health and Nutrition Examination Survey.

RESULTS

Among individuals aged 6-21 years, HBV prevalence decreased after 2011, from 0.72% in 1999-2004 and 0.85% in 2005-2010 to 0.27% in 2011-2016 (P < 0.001), whereas HCV prevalence increased to 0.26% in 2011-2016 after an initial decline from 0.15% in 1999-2004 to 0.02% in 2005-2010 (P = 0.01). Possible NAFLD prevalence also increased by approximately 40% in individuals aged 12-21 years, from 8.54% in 1999-2004 to 10.1% in 2005-2010 and then 11.8% in 2011-2016 (P = 0.033), with most possible NAFLD individuals being male, being obese, or having higher glucose, fasting insulin, hemoglobin A1c, homeostatic model assessment of insulin resistance, liver enzymes, lipids, and uric acid (all P < 0.01). On multivariate logistic regression, hypertension (odds ratio 4.79, 95% confidence interval 1.44-15.9) and dyslipidemia (odds ratio 11.6, 95% confidence interval 5.65-23.9) increased risk for possible NAFLD but not income:poverty ratio, hours spent on computer use, or added sugars.

DISCUSSION

Although HBV prevalence has decreased in recent years among US children and adolescents, HCV and possible NAFLD have increased. Public health efforts must seek further understanding of the driving factors of this increase so that age-appropriate interventions can be developed and implemented.

Adolescent Hepatitis C: Prevalence, Impact, and Management Challenges

The prevalence of Hepatitis C virus infection (HCV), a leading cause of chronic liver disease worldwide, is rising in the United States (US) and other high-income countries, especially among youth and young adults. This surge in cases is closely associated with the opioid crisis and intravenous drug use (IVDU). However, its prevalence and impact on the adolescent population have not been thoroughly studied and therefore is poorly understood. The pediatric population tends to have milder liver disease and progression when compared to adults; however, there is a risk of developing liver cirrhosis, in addition to facing decreased quality of life and stigmatization from the disease. The recent approval of direct-acting antiviral (DAA) regimens for all HCV genotypes and age greater than 3 years has revolutionized its management. Therapy has shifted from the prolonged interferon-based regimens, to shorter duration, once daily oral pills that are highly effective, curative and with fewer side effects. Therapy is now indicated for all adolescents with hepatitis C virus infection, regardless of stage of liver disease, recent IVDU, or coinfection with HIV, therefore eliminating a lifetime risk of chronic liver disease, cirrhosis and hepatocarcinoma. Nonetheless, adolescents are rarely tested or treated for hepatitis C infection, and very few adolescents complete therapy. Implementation of point of care (POC) testing of high-risk youth at drug treatment centers or other juvenile facilities may be a good strategy to increase testing, diagnosis and therapy. This review article aims to educate pediatricians and other primary care providers to help decrease the existing knowledge gap on the subject.

Progress and Barriers Towards Elimination of Chronic Hepatitis C in Children

Chronic hepatitis C (CHC) is a global health burden. Mother-to-child transmission (MTCT) accounts for most HCV infections in pediatric patients. Spontaneous viral clearance may occur in early childhood but is uncommon thereafter. Infection is usually asymptomatic during childhood, although without an effective treatment, vertically infected children may develop serious liver complications including cirrhosis and hepatocellular carcinoma in adulthood. Despite the lack of vaccine against hepatitis C and effective post-exposure methods of prevention of MTCT, treatment with direct-acting antiviral agents (DAAs) raised the prospect of eliminating HCV on a population level. Highly effective, well-tolerated, oral, and interferon-free regimens of short duration have revolutionized treatment of CHC. However, access to these therapies might be limited because of its high cost. In this review, we provide the current state of knowledge on the epidemiology, testing, monitoring and treating of HCV in children. We outline the remaining gaps in therapy and barriers to disease eradication.

Prevalence of and risk factors for hepatitis B and C viral co-infections in HIV infected children in Lagos, Nigeria

INTRODUCTION

The study was carried out to determine the prevalence of and risk factors for hepatitis B and C viral co-infections in HIV infected children in Lagos.

METHOD

A cross-sectional study conducted to determine the prevalence and risk factors for hepatitis B and C viral co-infection in children aged 2 months to 13 years. There were 187 HIV infected and 187 HIV naïve age, sex-matched controls. Blood samples of participants were assayed for the serologic markers [HBsAg, anti-HBc, and anti-HCV)] of HBV and HCV viral infections using the Enzyme-Linked Immunosorbent assay (ELISA) method.

RESULT

The prevalence of HBV infection using HBsAg was 5.3% and 4.8% (p = 0.814), among HIV-infected and HIV naïve children respectively, while using anti-HBc the prevalence was 7.0% and 7.5% (p = 0.842) among HIV- infected and HIV naïve children respectively. The prevalence of HCV infection among HIV- infected and HIV naive children were equal to 0.5% (p = 1.000). There was also no significant association with the identifiable risk factors (sharing of a toothbrush, sharing of needles, incision marks/tattoo, hepatitis B immunization status, history of blood transfusion, previous surgical operation, sexual exposure/abuse, history of jaundice, and genital circumcision) and the HBV and or HCV status among both groups of children. History of sexual exposure/abuse and history of jaundice were however found to be predictors of the presence of HBsAg among HIV infected children only, using a binary logistic regression model.

CONCLUSION

The prevalence of HBV and or HCV infection among HIV-infected children is similar to the prevalence among HIV naïve children, suggesting that HIV-infected children are not more predisposed to viral hepatitis than healthy children. Also, there was no significant difference in the prevalence of HBV infection irrespective of the use of HBsAg or anti-HBc.

Meeting the WHO hepatitis C virus elimination goal: Review of treatment in paediatrics

Over 3 million paediatric patients globally and ~50 000 in the United States are estimated to be infected with HCV. Eradicating HCV in children helps prevent liver fibrosis, cirrhosis and hepatocellular carcinoma; reduces extra-hepatic manifestations of HCV; improves quality of life; and increases survival. The 2019 American Association for the Study of Liver Diseases-Infectious Diseases Society of America (AASLD-IDSA) guidelines now recommend direct-acting antiviral (DAA) treatment with an approved regimen for all children and adolescents with HCV infection aged ≥3 years. We conducted a descriptive review of the new DAA treatments for HCV infection in the paediatric population. Ledipasvir/sofosbuvir (LDV/SOF) and sofosbuvir with ribavirin (SOF/RBV) are now approved for those ≥3 years old under specific clinical scenarios; sofosbuvir/velpatasvir (SOF/VEL) is the only pangenotypic agent approved for those ≥6 years or ≥17 kg, and glecaprevir/pibrentasvir (GLE/PIB) is approved for adolescents ≥12 years old or ≥45 kg. These DAA regimens are well-tolerated and have comparable sustained virologic response rates at 12 weeks post-treatment compared to those reported in adults (close to 100%). The introduction of DAAs has significantly changed the landscape of HCV treatment in adults and children with HCV infection and has increased confidence that the 2030 World Health Organization elimination goal may be attainable. Further studies are warranted to determine the optimal treatment for children with HCV infection, including timing, regimen and duration. Additionally, with the recent paediatric approvals, long-term safety data are needed.

Ombitasvir, Paritaprevir, Ritonavir, and Dasabuvir Mini-Tabs Plus Ribavirin for Children Aged 3-11 Years with Hepatitis C Genotype 1a

Introduction

To assess the safety, efficacy, and pharmacokinetics of mini-tablet formulations of ombitasvir (OBV), paritaprevir (PTV), ritonavir, and dasabuvir (DSV) with or without ribavirin for 12 weeks in children infected with chronic hepatitis C virus (HCV) genotype (GT) 1.

Methods

This is an ongoing, open-label, Phase 2/3 study in children 3–11 years old infected with HCV GT1 who were HCV treatment-naïve and non-cirrhotic. Pediatric mini-tablet formulations of OBV, PTV, ritonavir, and DSV plus ribavirin oral solution were administered for 12 weeks based on body weight. Endpoints included SVR12, adverse events (AEs), and pharmacokinetic parameters.

Results

Overall, 26 children received OBV, PTV, ritonavir, and DSV plus ribavirin; 14 were 3–8 years old and 12 were 9–11 years old; 35% were male; and all had chronic HCV GT1a infection. The SVR12 rate was 96% (25/26; 95% CI 81.1–99.3), with 1 child failing to achieve SVR12 due to non-adherence and treatment discontinuation. Treatment-emergent AEs of Grade ≥ 3 occurred in 3 children; 2 events in 1 child were considered serious; and none were considered treatment-related. No AEs led to discontinuation of study treatment. The most common AEs were headache (27%), fatigue (23%), pyrexia (19%), and vomiting (19%). Pharmacokinetic results showed mini-tablet formulations of OBV, PTV, DSV, and ritonavir drug exposures were comparable to the adult formulation.

Conclusion

The mini-tablet combination of OBV, PTV, ritonavir, and DSV plus ribavirin to treat HCV GT1a infection for 12 weeks was highly effective and suitable in children 3–11 years of age.

Trial Registration

ClinicalTrials.gov identifier, NCT02486406.

Electronic supplementary material

The online version of this article (10.1007/s12325-020-01389-9) contains supplementary material, which is available to authorized users.

Generic sofosbuvir/ledipasvir for the treatment of genotype 4 chronic hepatitis C in Egyptian children (9-12 years) and adolescents

BACKGROUND/PURPOSE OF THE STUDY

Worldwide and national efforts are directed against eradication of HCV. The introduction of direct-acting antivirals (DAAs) has changed dramatically the outcome of HCV treatment. In spite of the Food and Drug Administration approval of the oral drugs sofosbuvir (SOF) and ledipasvir (LED) for the treatment of HCV in adolescents more than or equal to 12 years old, sufficient real-world experience is still lacking. The aim of this study was to assess the safety and efficacy of the generic SOF/LED fixed-dose combination 400/90 (400 mg SOF + 90 mg LED) for the treatment of adolescents and children (9-12 years) with chronic hepatitis C (CHC).

METHODS

In this prospective observational study, 100 cases of genotype 4 CHC were recruited consecutively from those fulfilling the inclusion and exclusion criteria. All cases received the generic fixed-dose combination SOF/LED (400/90), one tablet daily for 12 weeks. All clinical, laboratory, and virologic characteristics were evaluated at base line, and week (W) 2, 4, 8, and 12 of therapy and W12 post-treatment (SVR12).

RESULTS

Recruited children (9-12) and adolescents weighed 28-83 and 31-90 kg, respectively. Eighty cases were naïve and 20 cases were pegylated interferon/ribavirin treatment-experienced. Very rapid virologic response (vRVR) at W2 was 96%, while at W4 response rate was 100% and maintained till the end of treatment and at W12 post-treatment (SVR12). All reported side effects were mild and did not lead to treatment termination and disappeared at W12 post-treatment.

CONCLUSION

The generic SOF/LED fixed-dose combination is safe and effective in children, 9-12 years, and adolescents with vRVR rate of 96%, 100% EOT response and SVR12.

Paediatric hepatitis C virus infection and its treatment: Present, past, and future

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease in the world. It is a challenging medico-social problem in the paediatric population. High HCV infection rates are reported in low and middle incomes countries. From the health economic point of view treatment of hepatitis C virus (HCV) with subsequent virus eradication is very effective as it eliminates the long-term sequelae of untreated or maltreated HCV. In this review we summarize the updates and highlight the historical approach of treatment of chronic HCV infection in children in the new era of directly acting antiviral (DAA) agents.

Cost Effectiveness of Early Treatment with Direct-Acting Antiviral Therapy in Adolescent Patients with Hepatitis C Virus Infection

OBJECTIVE

To evaluate the cost effectiveness of early treatment with direct-acting antiviral therapy in adolescent patients with chronic hepatitis C virus (HCV) infection compared with treatment deferral.

STUDY DESIGN

We constructed a Markov model to assess the cost effectiveness of treating a hypothetical cohort of 30 000 adolescent patients with chronic HCV at age 12 years compared with deferring treatment until adulthood from a societal perspective. Model inputs for transition probabilities, HCV treatment and medical care costs, and quality-adjusted life-year (QALY) utilities were derived from the literature and wholesale acquisition estimates. Deterministic sensitivity analyses varied parameters for non-HCV medical care and treatment cost, reinfection rates, treatment uptake, disease progression, liver transplant survival, and treatment with recently approved pangenotypic direct-acting antiviral agents. Discounted costs and total QALYs per person were quantified after 30 years. Cost effectiveness was evaluated as the incremental change in total medical costs per QALY gained.

RESULTS

The incremental cost effectiveness of early treatment initiation compared with deferred treatment was approximately $27 000 per QALY gained after 30 years and considered cost effective. In a scenario analysis, hypothetical treatment initiation with currently available pangenotypic agents would be even more cost effective, ranging from $10 000 to $21 000 per QALY gained. Cost-effectiveness estimates were sensitive to variations in decompensated cirrhosis progression in adolescence, adult reinfection, and treatment uptake in adults.

CONCLUSIONS

Early treatment in adolescent patients with chronic HCV infection with currently available direct-acting antivirals seems to be cost effective compared with deferred treatment. Future efforts to control the HCV epidemic should include increasing the number of children treated.

Epidemiology and natural history of hepatitis C virus infection among children and young people

BACKGROUND & AIMS

Chronic hepatitis C virus (HCV) infection is a global health burden. Although HCV infection rarely contributes to morbidity during childhood, most HCV-infected children develop chronic HCV with a lifetime risk of liver disease. Little is known about the development of long-term liver disease and the effect of treatment in patients infected with HCV in childhood.

METHOD

This study was a retrospective review of patients infected with HCV in childhood enrolled in HCV Research UK. A total of 1,049 patients were identified and included.

RESULTS

The main routes of infection were intravenous drug use (53%), blood product exposure (24%) and perinatal infection (11%). Liver disease developed in 32% of patients, a median of 33 years after infection, irrespective of the mode of infection. Therefore, patients with perinatal exposure developed cirrhosis at an earlier age than the rest of the risk groups. The incidence of hepatocellular carcinoma (HCC) was 5%, liver transplant 4% and death occurred in 3%. Overall, 663 patients were treated (55% with interferon/pegylated interferon and 40% with direct-acting antivirals). Sustained virological response (SVR) was achieved in 406 (75%). There was a higher mortality rate among patients without SVR vs. those with SVR (5% vs. 1%, p = 0.003). Treatment was more effective in patients without cirrhosis and disease progression was less frequent (13%) than in patients with cirrhosis at the time of therapy (28%) p < 0.001. Patients with cirrhosis were more likely to develop HCC, require liver transplantation, or die.

CONCLUSION

HCV infection in young people causes significant liver disease, which can now be prevented with antiviral therapy. Early treatment, especially before development of cirrhosis is essential. Detection of HCV should be aimed at relevant risk groups and antiviral therapy should be made available in childhood to prevent long-term liver disease and spread of HCV.

LAY SUMMARY

Chronic hepatitis C virus (HCV) infection is a global health problem, which can now be treated with potent direct-acting antiviral drugs. This study demonstrates that HCV infection in childhood causes serious liver disease in 32% of patients, a median of 33 years after infection, irrespective of age, mode and route of infection. Disease outcomes were better in patients treated before the development of advanced liver disease. Antiviral therapy should be made available in childhood to prevent long-term liver disease and the spread of HCV.

Childhood Fructoholism and Fructoholic Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is an emerging entity, becoming the most prevalent pediatric chronic liver disease. Its broad spectrum of histological findings, comorbidities, and complications, including cirrhosis and liver failure, can occur in childhood, emphasizing the severity of pediatric NAFLD. Current lifestyle and diet modifications have been linked to the increasing prevalence of NAFLD, including the rise of fructose consumption, a monosaccharide present in foods that contain added sugar, such as sugar‐sweetened beverages. Excessive fructose consumption is believed to cause addiction like alcohol and other drugs. As such, the new term “fructoholism” refers to the consumption of a substance (fructose) that can cause psychological and physical damage and become a major public health concern, highlighting the seriousness of the excessive consumption of fructose in the pediatric age. Hepatic fructose metabolization leads to hepatic steatosis and progression to fibrosis through mechanisms comparable to alcoholic liver disease, hence the term “fructoholic liver disease.” Conclusion: The importance of implementing reliable global strategies, such as education campaigns to promote healthy diet, increasing taxes on foods that contain added sugars, subsidies to promote accessibility to fruit and vegetables, and strict food industry regulation to reduce sugar intake in children and adolescents, cannot be overemphasized.

Hepatitis C virus infection in children in the era of direct-acting antiviral

Hepatitis C virus (HCV) infection remains an important global health problem with chronic infection affecting approximately 11 million children worldwide. The emergence of direct-acting antiviral (DAA) therapies and the development of non-invasive methods for the determination of liver fibrosis will significantly improve the management of paediatric patients with chronic HCV infection in subsequent years. For paediatric patients, a new era of highly effective DAA agents is beginning, and the first results of available clinical trials are very promising. In this era, the identification and monitoring of patients continues to be an important issue. The availability of non-invasive serological and imaging methods to measure hepatic fibrosis enables the identification of patients with significant or advanced liver fibrosis stages. This article summarizes the current data on the epidemiology and progress of research aimed to evaluate the new therapies and non-invasive methods for liver injury in paediatric patients with chronic hepatitis C.

Quality of life in adolescents with hepatitis C treated with sofosbuvir and ribavirin

Chronic HCV infection has been associated with impairment of HRQL in both adults and paediatric patients. Our aim was to assess the HRQL of HCV-positive children treated with SOF + RBV. The data for this post hoc analysis were collected in a phase 2 open-label multinational study that evaluated safety and efficacy of SOF (400 mg/day) plus RBV (weight-based up to 1400 mg/day) for 12 or 24 weeks in adolescents with chronic HCV (GS-US-334-1112). Patients and their parents/guardians completed the PedsQL-4.0-SF-15 questionnaire at baseline, at the end of treatment and in post-treatment follow-up. We included 50 adolescents with HCV genotype 2 and 3 without cirrhosis (14.8 ± 1.9 years; male: 58%; treatment-naïve: 82%; vertically transmitted HCV: 70%). After treatment, 100% of patients with HCV genotype 2 and 95% with genotype 3 achieved SVR-12. During treatment with SOF + RBV, there were no significant decrements in any of patients' self-reported or parent-proxy-reported PRO scores regardless of treatment duration (all P > .05). After treatment cessation, we recorded a statistically significant improvement in patients' self-reported Social Functioning score by post-treatment week 12: on average, +4.8 points on a 0-100 scale (P = .02). By post-treatment week 24, parent-proxy-reported School Functioning score increased by, on average, +13.0 points (P = .0065). In multivariate analysis, history of abdominal pain and psychiatric disorders were predictive of impaired HRQL in adolescents with HCV (P < .05). Adolescents with HCV do not seem to experience any HRQL decrement during treatment with SOF + RBV and experience some improvement of their HRQL scores after achieving SVR.

Hepatitis C virus in children: the global picture

Chronic hepatitis C virus (HCV) infection is a major cause of cirrhosis, hepatocellular carcinoma and end-stage liver disease. One hundred thirty million to 150 million people have chronic HCV infection, among them 11 million are younger than 15 years of age. This review summarises the epidemiology and characteristics of HCV infection in children, and highlights the role of the new upcoming therapies in HCV-related liver complications.

Peginterferon Therapy in Children With Chronic Hepatitis C: A Nationwide, Multicenter Study in Japan, 2004-2013

OBJECTIVES

The aim of the present study was to review the medical treatment of Japanese children and adolescents with chronic hepatitis C in the past 10 years.

METHODS

This nationwide, multicenter study evaluated patients who were younger than 18 years of age when diagnosed with chronic hepatitis C virus (HCV) infection and were treated with pegylated interferon (PEG-IFN) monotherapy or PEG-IFN/ribavirin (RBV) combination therapy between 2004 and 2013. The subjects' median age was 10 (3-18) years, with a male to female ratio of 52:50 and a genotype-1 to genotype-2 ratio of 45:57. Among the 102 patients, 18 received PEG-IFN monotherapy and 84 received PEG-IFN/RBV combination therapy. The IL28B genotype polymorphism was analyzed in patients infected with genotype-1.

RESULTS

In patients with HCV genotype-1 infections, sustained virological response (SVR) rates obtained by PEG-IFN monotherapy and by PEG-IFN/RBV combination therapy were 100% (2/2) and 72% (31/43), respectively. In patients with HCV genotype-2 infections, SVRs were 75% (12/16) and 100% (41/41), respectively. In 32 genotype-1 patients available for the IL28B genotype (rs8099917), SVR was achieved in more patients in the IL28B major allele group than in the minor allele group (15/17 vs 7/15, P = 0.021) after PEG-IFN/RBV combination therapy. The frequencies of adverse events were similar between the treatment regimens.

CONCLUSIONS

Overall, both therapies showed encouraging results, and were reasonably safe in children and adolescents with chronic hepatitis C. The IL28B genotype was useful for predicting the treatment response to PEG-IFN/RBV combination therapy in this cohort.

Infectious Diseases and the Kidney in Children

The kidney is involved in a wide range of bacterial, viral, fungal, and parasitic diseases. In most systemic infections, renal involvement is a minor component of the illness, but in some, renal failure may be the presenting feature and the major problem in management. Although individual infectious processes may have a predilection to involve the renal vasculature, glomeruli, interstitium, or collecting systems, a purely anatomic approach to the classification of infectious diseases affecting the kidney is rarely helpful because most infections may involve several different aspects of renal function. In this chapter, a microbiological classification of the organisms affecting the kidney is adopted. Although they are important causes of renal dysfunction in infectious diseases, urinary tract infections and hemolytic uremic syndrome (HUS) are not discussed in detail because they are considered separately in chapters XX and XX, respectively.