Tick-borne infections in children in North America.

PURPOSE OF REVIEW: Because both incidence and awareness of tick-borne infections is increasing, review of major infections and recent advances related to their diagnosis and management is important. RECENT FINDINGS: A new algorithm, termed modified two-tier testing, for testing for antibodies to Borrelia burgdorferi , the cause of Lyme disease, has been approved and may replace traditional two-tier testing. In addition, doxycycline is now acceptable to use for treatment of and/or prophylaxis for Lyme disease for up to 21 days in children of any age. Borrelia miyamotoi , a bacterium in the relapsing fever type of Borrelia, is the first of this type of Borrelia that is transmitted by hard-bodied ticks such as Ixodes scapularis. SUMMARY: Awareness of these infections and advances in their diagnosis and treatment is important to assure the best outcomes for affected patients. Table 1 contains a summary of infections discussed.

Pilot study of a parent-based intervention for functional somatic symptoms in children.

OBJECTIVE: Functional somatic symptoms are associated with significant distress and impairment for children and their families. Despite the central role that families play in their children's care, there is little clinical research to guide how parents can support their children with functional somatic symptoms and promote better functioning. To address this gap, we developed a parent-based intervention for functional somatic symptoms in children and obtained preliminary data on acceptability, feasibility, treatment satisfaction, and clinical outcomes. METHOD: The intervention was adapted from SPACE (Supportive Parenting for Anxious Childhood Emotions), an evidence-based treatment for anxiety and related disorders in children. The intervention, SPACE-Somatic, was delivered to parents of 16 children (Mage = 14.50 years; 75% girls) with a range of functional somatic symptoms. Parents participated in seven weekly group sessions conducted via telehealth. RESULTS: We found that SPACE-Somatic was acceptable, feasible, and satisfactory to parents. There were significant improvements in several clinical outcomes from baseline to posttreatment, including children's level of functional impairment, with some gains maintained at 3-month follow-up. Parents also reported improvements in their own stress and their accommodation of children's symptoms. CONCLUSION: This pilot study provides preliminary evidence that a parent-based intervention is viable and beneficial to children with functional somatic symptoms and their parents.

Understanding the Factors Influencing Health Care Provider Recommendations about Adolescent Vaccines: A Proposed Framework.

Health care provider recommendations are among the most important factors influencing parents' decisions to vaccinate their adolescents. However, delivery of high-quality health care provider recommendations for vaccination is not universal. There is wide variation in the strength, timeliness and consistency of the delivery of recommendations for all adolescent vaccines. The factors that influence health care providers' recommendations are multi-level and can be conceptualized in much the same way as vaccine acceptance among parents. Health care providers are influenced by their own attitudes and beliefs about a vaccine and also by the patient they are treating and by the community in which they practice as well as state and national level vaccine policy. We propose a multi-level framework for understanding the factors that influence health care providers' recommendations at the individual, interpersonal and community level to both develop and adapt interventions to improve providers' recommendations.

The Effectiveness of Varicella Vaccine: 25 Years of Postlicensure Experience in the United States.

We summarize studies of varicella vaccine's effectiveness for prevention of varicella and lessons learned during the first 25 years of the varicella vaccination program in the United States. One dose of varicella vaccine provided moderate protection (82%-85%) against varicella of any severity and high protection (100%) against severe varicella, with some waning of protection over time. The 1-dose program (1995-2006) had a substantial impact on the incidence both of varicella and of severe outcomes (71%-90% decrease) although it did not prevent low-level community transmission and some outbreaks continued to occur in highly vaccinated populations. Two doses of varicella vaccine improved the vaccine's effectiveness by at least 10% against varicella of any severity, with further declines in the incidence both of varicella and of severe outcomes as well as in both number and size of outbreaks. There is no evidence for waning of the effectiveness of 2 doses of the vaccine.

Live Attenuated Varicella Vaccine: Prevention of Varicella and of Zoster.

Michiaki Takahashi developed the live attenuated varicella vaccine in 1974 . This was the first, and is still the only, herpesvirus vaccine. Early studies showed promise, but the vaccine was rigorously tested on immunosuppressed patients because of their high risk of fatal varicella; vaccination proved to be lifesaving. Subsequently, the vaccine was found to be safe and effective in healthy children. Eventually, varicella vaccine became a component of measles mumps rubella vaccine, 2 doses of which are administered in the USA to ~90% of children. The incidence of varicella has dropped dramatically in the USA since vaccine-licensure in 1995. Varicella vaccine is also associated with a decreased incidence of zoster and is protective for susceptible adults. Today, immunocompromised individuals are protected against varicella due to vaccine-induced herd immunity. Latent infection with varicella zoster virus occurs after vaccination; however, the vaccine strain is impaired for its ability to reactivate.

Patterns of recommended vaccine receipt among women ages 24-45 years: a cross-sectional analysis.

BACKGROUND: Vaccine receipt among mid-adults remains low, with only one quarter of adults being up to date for all recommended vaccines. It is important to understand the myriad factors that influence vaccine receipt among mid-adult women to address these low rates. METHODS: We conducted a cross-sectional analysis of data from women ages 24-45 years collected as part of an ongoing case-control study of the effectiveness of HPV vaccine. We examined associations between demographic characteristics and healthcare utilization and receipt of individual vaccines and combinations of multiple vaccines using logistic regression analyses for three routinely recommended vaccines: tetanus, influenza and HPV. RESULTS: Among the 309 women enrolled in the study, only 19 (6.2%) were up to date for all three recommended vaccines and 41 (13.3%) had not received any of the recommended vaccines. A greater number of health care visits in the past year was associated with receipt of influenza (aOR = 6.37, 95% CI = 2.53, 16.1) and tetanus (aOR = 2.17, 95% CI = 1.14, 4.12) vaccines. White women were more likely to have received HPV vaccine (aOR = 2.39, 95% CI = 1.07, 5.36). CONCLUSIONS: Uptake of recommended vaccines is low among young and mid-adult women. There is a need for greater understanding of the underlying factors influencing vaccine receipt in this population.

Parents' Perspectives on Communication and Shared Decision Making for Febrile Infants ≤60 Days Old.

OBJECTIVES: Decisions about the management of febrile infants ≤60 days old may be well suited for shared decision making (SDM). Our objectives were to learn about parents' experiences with receiving and understanding information in the emergency department (ED) and their perspectives on SDM, including for decisions about lumbar puncture (LP). METHODS: We conducted semistructured interviews with 23 parents of febrile infants ≤60 days old evaluated in the pediatric ED at an urban, academic medical center. Interviews assessed parents' experiences in the ED and their perspectives on communication and SDM. Two investigators coded the interview transcripts, refined codes, and identified themes using the constant comparative method. RESULTS: Parents' unmet need for information negatively impacted parents' understanding, stress, and trust in the physician. Themes for parents' perspectives on SDM included the following: (1) giving parents the opportunity to express their opinions and concerns builds confidence in the decision making process, (2) parents' preferences for participation in decision making vary considerably, and (3) different perceptions about risks influence parents' preferences about having their infant undergo an LP. Although some parents would defer decision making to the physician, they still wanted to be able to express their opinions. Other parents wanted to have the final say in decision making. Parents valued risks and benefits of having their child undergo an LP differently, which influenced their preferences. CONCLUSIONS: Physicians need to adequately inform parents to facilitate parents' understanding of information and gain their trust. Shared decision making may be warranted for decisions about whether to perform an LP, although parents' preferences for participating in decision making vary.

Prospective Evaluation of the Frequency and Severity of Symptoms in Lyme Disease Patients With Erythema Migrans Compared With Matched Controls at Baseline, 6 Months, and 12 Months.

BACKGROUND: Erythema migrans is the most common clinical manifestation of Lyme disease. Despite antibiotic therapy, typically at least 10% of adult patients with erythema migrans experience persistence of at least 1 subjective symptom for ≥6 months (posttreatment Lyme disease symptoms [PTLDS]). METHODS: This study was designed to determine whether the frequency and severity (based on a visual analogue scale) of 12 particular symptoms in patients with erythema migrans (n = 52) differed from matched control subjects (n = 104) followed prospectively for 12 months. RESULTS: At baseline, patients with Lyme disease were more likely than controls to have at least 1 symptom (P = .006). Among symptomatic subjects, Lyme disease patients had a higher mean number of symptoms (P < .001) and a higher mean total symptom severity score (P < .001). At both 6 and 12 months, however, there were no significant differences for these variables and no significant differences in the frequency or severity of any of the 12 individual symptoms assessed. However, 10 patients were clinically assessed as having possible PTLDS. CONCLUSIONS: Patients with erythema migrans were more likely than matched control subjects to be symptomatic at baseline with a greater symptom severity score, but this was not found at ≥6 months. Use of symptom survey data alone, however, was less likely to identify patients with possible PTLDS compared with individual clinical assessments. Because it is very challenging to be certain that the presence of long-term symptoms in a particular patient is correctly attributable to having had Lyme disease, an objective biomarker would be highly desirable.

Estimating the population-level impact of vaccines using synthetic controls.

When a new vaccine is introduced, it is critical to monitor trends in disease rates to ensure that the vaccine is effective and to quantify its impact. However, estimates from observational studies can be confounded by unrelated changes in healthcare utilization, changes in the underlying health of the population, or changes in reporting. Other diseases are often used to detect and adjust for these changes, but choosing an appropriate control disease a priori is a major challenge. The "synthetic controls" (causal impact) method, which was originally developed for website analytics and social sciences, provides an appealing solution. With this approach, potential comparison time series are combined into a composite and are used to generate a counterfactual estimate, which can be compared with the time series of interest after the intervention. We sought to estimate changes in hospitalizations for all-cause pneumonia associated with the introduction of pneumococcal conjugate vaccines (PCVs) in five countries in the Americas. Using synthetic controls, we found a substantial decline in hospitalizations for all-cause pneumonia in infants in all five countries (average of 20%), whereas estimates for young and middle-aged adults varied by country and were potentially influenced by the 2009 influenza pandemic. In contrast to previous reports, we did not detect a decline in all-cause pneumonia in older adults in any country. Synthetic controls promise to increase the accuracy of studies of vaccine impact and to increase comparability of results between populations compared with alternative approaches.

Differences in the Impact of Pneumococcal Serotype Replacement in Individuals With and Without Underlying Medical Conditions.

BACKGROUND: Pneumococcal conjugate vaccines (PCVs) have had a well-documented impact on the incidence of invasive pneumococcal disease (IPD). However, declines in IPD due to vaccine-targeted serotypes have been partially offset by increases in IPD due to nonvaccine serotypes (NVTs). The goal of this study was to quantify serotype-specific changes in the incidence of IPD that occurred in different age groups, with or without certain comorbidities, following the introduction of 7-valent pneumococcal conjugate vaccine (PCV7) and 13-valent pneumococcal conjugate vaccine (PCV13) in the childhood vaccination program in Denmark. METHODS: We used nationwide surveillance data for IPD and a hierarchical Bayesian regression framework to estimate changes in the incidence of IPD associated with the introduction of PCV7 (2007) and PCV13 (2010) while controlling for serotype-specific epidemic cycles and unrelated secular trends. RESULTS: Following the introduction of PCV7 and PCV13 in children, the net impact of serotype replacement varied considerably by age group and comorbidities. Differences in the magnitude of serotype replacement were due to variations in the incidence of NVTs in the different risk groups before the introduction of PCVs. The relative increases in the incidence of IPD caused by specific NVTs did not differ appreciably between risk groups in the postvaccination period. Serotype replacement offset a greater proportion of the benefit of PCVs in strata in which the NVTs comprised a larger proportion of cases prior to the introduction of the vaccines. CONCLUSIONS: These findings could help to predict the impact of next-generation PCVs in specific risk groups.

Epidemiology and Etiology of Invasive Bacterial Infection in Infants ≤60 Days Old Treated in Emergency Departments.

OBJECTIVES: To help guide empiric treatment of infants ≤60 days old with suspected invasive bacterial infection by describing pathogens and their antimicrobial susceptibilities. STUDY DESIGN: Cross-sectional study of infants ≤60 days old with invasive bacterial infection (bacteremia and/or bacterial meningitis) evaluated in the emergency departments of 11 children's hospitals between July 1, 2011 and June 30, 2016. Each site's microbiology laboratory database or electronic medical record system was queried to identify infants from whom a bacterial pathogen was isolated from either blood or cerebrospinal fluid. Medical records of these infants were reviewed to confirm the presence of a pathogen and to obtain demographic, clinical, and laboratory data. RESULTS: Of the 442 infants with invasive bacterial infection, 353 (79.9%) had bacteremia without meningitis, 64 (14.5%) had bacterial meningitis with bacteremia, and 25 (5.7%) had bacterial meningitis without bacteremia. The peak number of cases of invasive bacterial infection occurred in the second week of life; 364 (82.4%) infants were febrile. Group B streptococcus was the most common pathogen identified (36.7%), followed by Escherichia coli (30.8%), Staphylococcus aureus (9.7%), and Enterococcus spp (6.6%). Overall, 96.8% of pathogens were susceptible to ampicillin plus a third-generation cephalosporin, 96.0% to ampicillin plus gentamicin, and 89.2% to third-generation cephalosporins alone. CONCLUSIONS: For most infants ≤60 days old evaluated in a pediatric emergency department for suspected invasive bacterial infection, the combination of ampicillin plus either gentamicin or a third-generation cephalosporin is an appropriate empiric antimicrobial treatment regimen. Of the pathogens isolated from infants with invasive bacterial infection, 11% were resistant to third-generation cephalosporins alone.

Missed opportunities for HPV immunization among young adult women.

BACKGROUND: Despite the availability of a safe and efficacious vaccine against human papillomavirus, uptake of the vaccine in the United States is low. Missed clinical opportunities to recommend and to administer human papillomavirus vaccine are considered one of the most important reasons for its low uptake in adolescents; however, little is known about the frequency or characteristics of missed opportunities in the young adult (18-26 years of age) population. OBJECTIVE: The objective of the study was to assess both the rates of and the factors associated with missed opportunities for human papillomavirus immunization among young adult women who attended an urban obstetrics and gynecology clinic. STUDY DESIGN: In this cross-sectional study, medical records were reviewed for all women 18-26 years of age who were underimmunized (<3 doses) and who sought care from Feb. 1, 2013, to January 31, 2014, at an urban, hospital-based obstetrics and gynecology clinic. A missed opportunity for human papillomavirus immunization was defined as a clinic visit at which the patient was eligible to receive the vaccine and a dose was due but not administered. Multivariable logistic regression was used to test associations between sociodemographic variables and missed opportunities. RESULTS: There were 1670 vaccine-eligible visits by 1241 underimmunized women, with a mean of 1.3 missed opportunities/person. During the study period, 833 of the vaccine eligible women (67.1%) had at least 1 missed opportunity. Overall, the most common types of visits during which a missed opportunity occurred were postpartum visits (17%) or visits for either sexually transmitted disease screening (21%) or contraception (33%). Of the patients with a missed opportunity, 26.5% had a visit at which an injectable medication or a different vaccine was administered. Women who identified their race as black had higher adjusted odds of having a missed opportunity compared with white women (adjusted odds ratio, 1.61 [95% confidence interval, 1.08-2.41], P < .02). Women who reported a non-English- or non-Spanish-preferred language had lower adjusted odds of having a missed opportunity (adjusted odds ratio, 0.25 [95% confidence interval, 0.07-0.87], P = .03). No other patient characteristics assessed in this study were significantly associated with having a missed opportunity. CONCLUSION: A majority of young-adult women in this study had missed opportunities for human papillomavirus immunization, and significant racial disparity was observed. The greatest frequency of missed opportunities occurred with visits for either contraception or for sexually transmitted disease screening.

Mindfulness-Based Stress Reduction for Adolescents with Functional Somatic Syndromes: A Pilot Cohort Study.

OBJECTIVE: To assess the feasibility of a mindfulness-based stress reduction (MBSR) program for adolescents with widespread chronic pain and other functional somatic symptoms and to make preliminary assessments of its clinical utility. STUDY DESIGN: Three cohorts of subjects completed an 8-week MBSR program. Child- and parent-completed measures were collected at baseline and 8 and 12 weeks later. Measures included the Functional Disability Inventory (FDI), the Fibromyalgia/Symptom Impact Questionnaire-Revised (FIQR/SIQR), the Pediatric Quality of Life Inventory, the Multidimensional Anxiety Scale (MASC2), and the Perceived Stress Scale. Subjects and parents were interviewed following the program to assess feasibility. RESULTS: Fifteen of 18 subjects (83%) completed the 8-week program. No adverse events occurred. Compared with baseline scores, significant changes were found in mean scores on the FDI (33% improvement, P = .026), FIQR/SIQR (26% improvement, P = .03), and MASC2 (child: 12% improvement, P = .02; parent report: 17% improvement, P = .03) at 8 weeks. MASC2 scores (child and parent) and Perceived Stress Scale scores were significantly improved at 12 weeks. More time spent doing home practice was associated with better outcomes in the FDI and FIQR/SIQR (44% and 26% improvement, respectively). Qualitative interviews indicated that subjects and parents reported social support as a benefit of the MBSR class, as well as a positive impact of MBSR on activities of daily living, and on pain and anxiety. CONCLUSIONS: MBSR is a feasible and acceptable intervention in adolescents with functional somatic syndromes and has preliminary evidence for improving functional disability, symptom impact, and anxiety, with consistency between parent and child measures. TRIAL REGISTRATION: ClinicalTrials.gov: NCT02190474.

Influenza-like illness in an urban community of Salvador, Brazil: incidence, seasonality and risk factors.

BACKGROUND: Our understanding of the epidemiology of influenza is limited in tropical regions, which in turn has hampered identifying optimal region-specific policy to diminish disease burden. Influenza-like illness (ILI) is a clinical diagnosis that can be used as a surrogate for influenza. This study aimed to define the incidence and seasonality of ILI and to assess its association with climatic variables and school calendar in an urban community in the tropical region of Salvador, Brazil. METHODS: Between 2009 and 2013, we conducted enhanced community-based surveillance for acute febrile illnesses (AFI) among patients ≥ 5 years of age in a slum community emergency unit in Salvador, Brazil. ILI was defined as a measured temperature of ≥ 37.8 °C or reported fever in a patient with cough or sore throat for ≤ 7 days, and negative test results for dengue and leptospirosis. Seasonality was analyzed with a harmonic regression model. Negative binomial regression models were used to correlate ILI incidence with rainfall, temperature, relative humidity and the number of days per month that schools were in session while controlling for seasonality. RESULTS: There were 2,651 (45.6% of 5,817 AFI patients) ILI cases with a mean annual incidence of 60 cases/1,000 population (95% CI 58-62). Risk of ILI was highest among 5-9 year olds with an annual incidence of 105 cases/1,000 population in 2009. ILI had a clear seasonal pattern with peaks between the 35-40th week of the year. ILI peaks were higher and earlier in 5-9 year olds compared with > 19 year olds. No association was seen between ILI and precipitation, relative humidity or temperature. There was a significant association between the incidence of ILI in children 5-9 years of age and number of scheduled school days per month. CONCLUSIONS: We identified a significant burden of ILI with distinct seasonality in the Brazilian tropics and highest rates among young school-age children. Seasonal peaks of ILI in children 5-9 years of age were positively associated with the number of school days, indicating that children may play a role in the timing of seasonal influenza transmission.

Parents' Recall and Reflections on Experiences Related to HPV Vaccination for Their Children.

Human papillomavirus (HPV) vaccination coverage remains suboptimal in the United States. We conducted in-depth interviews with parents of adolescents from an urban primary care center serving a low-income minority population to describe their experiences. We identified the following themes: (a) parents of unvaccinated children generally had not discussed the vaccine with providers and had low awareness; (b) among unaware parents, provision of brief information generally resulted in positive comments about the vaccine; (c) vaccine was typically not requested by parents but rather offered by providers; (d) strength of the recommendations from providers varied, and vaccine was sometimes presented as optional or low priority; (e) parents had low awareness of the three-dose regimen and poor recall about completion; and (f) limited understanding of why boys should be vaccinated. More than 7 years after the introduction of HPV vaccine, there is substantial room for improving the way it is recommended and discussed by providers.

"It All Depends": A Qualitative Study of Parents' Views of Human Papillomavirus Vaccine for their Adolescents at Ages 11-12 years.

Routine vaccination with three doses of human papillomavirus (HPV) vaccine is recommended for adolescent girls and boys at 11 or 12 years of age; however, vaccine uptake remains suboptimal. To understand the reasons why parents may accept or refuse HPV vaccine for their children at age 11 or 12 years, we conducted a qualitative study. Semi-structured interviews were conducted with parents or guardians (n = 45) whose adolescents receive care at an urban, hospital-based primary care practice. Data were analyzed using an iterative thematic approach. We found that many parents expressed high levels of support for HPV vaccine, including a majority who agreed with vaccination at age 11-12 years. Parents recognized that for prevention of consequences of HPV infection, vaccination of their child early in adolescence was desirable conceptually. However, many parents also expressed that in practice, HPV vaccine should be given to adolescents at the onset of sexual activity, a perception that led to preferences to delay administration of HPV vaccine among certain parents. These apparently contradictory views indicate the need for interventions focused on the benefits of vaccination at the recommended ages. Our findings may be useful in providers' discussions with parents about the vaccine, as pediatric and adolescent health care providers have the unique opportunity to educate parents and clarify misconceptions about vaccination.

Unorthodox alternative therapies marketed to treat Lyme disease.

BACKGROUND: Some patients with medically unexplained symptoms or alternative medical diagnoses suspect that they chronically suffer from the tick-borne infection Lyme disease. These patients are commonly targeted by providers of alternative therapies. This study was designed to identify and characterize the range of unorthodox alternative therapies advertised to patients with a diagnosis of Lyme disease. METHODS: Internet searches using the Google search engine were performed to identify the websites of clinics and services that marketed nonantimicrobial therapies for Lyme disease. We subsequently used the PubMed search engine to identify any scientific studies evaluating such treatments for Lyme disease. Websites were included in our review so long as they advertised a commercial, nonantimicrobial product or service that specifically mentioned utility for Lyme disease. Websites with patient testimonials (such as discussion groups) were excluded unless the testimonial appeared as marketing on a commercial site. RESULTS: More than 30 alternative treatments were identified, which fell into several broad categories: these included oxygen and reactive oxygen therapy; energy and radiation-based therapies; nutritional therapy; chelation and heavy metal therapy; and biological and pharmacological therapies ranging from certain medications without recognized therapeutic effects on Borrelia burgdorgeri to stem cell transplantation. Review of the medical literature did not substantiate efficacy or, in most cases, any rationale for the advertised treatments. CONCLUSIONS: Providers of alternative therapies commonly target patients who believe they have Lyme disease. The efficacy of these unconventional treatments for Lyme disease is not supported by scientific evidence, and in many cases they are potentially harmful.

Update on persistent symptoms associated with Lyme disease.

PURPOSE OF REVIEW: Lyme disease, caused by Borrelia burgdorferi, is the most common vector-borne illness in the United States. The pathogenesis, ecology, and epidemiology of Lyme disease have been well described, and antimicrobial treatment is very effective. There has been controversy about whether infection can persist and cause chronic symptoms despite treatment with antimicrobials. This review summarizes recent studies that have addressed this issue. RECENT FINDINGS: The pathogenesis of persistent nonspecific symptoms in patients who were treated for Lyme disease is poorly understood, and the validity of results of attempts to demonstrate persistent infection with B. burgdorferi has not been established. One study attempted to use xenodiagnosis to detect B. burgdorferi in patients who have been treated for Lyme disease. Another study assessed whether repeated episodes of erythema migrans were due to the same or different strains of B. burgdorferi. A possible cause of persistent arthritis in some treated patients is slow clearance of nonviable organisms that may lead to prolonged inflammation. The results of all of these studies continue to provide evidence that viable B. burgdorferi do not persist in patients who receive conventional antimicrobial treatment for Lyme disease. SUMMARY: Patients with persistent symptoms possibly associated with Lyme disease often provide a challenge for clinicians. Recent studies have provided additional evidence that viable B. burgdorferi do not persist after conventional treatment with antimicrobials, indicating that ongoing symptoms in patients who received conventional treatment for Lyme disease should not be attributed to persistent active infection.

Factor VIII May Predict Catheter-Related Thrombosis in Critically Ill Children: A Preliminary Study.

OBJECTIVE: If we can identify critically ill children at high risk for central venous catheter-related thrombosis, then we could target them for pharmacologic thromboprophylaxis. We determined whether factor VIII activity or G value was associated with catheter-related thrombosis in critically ill children. DESIGN: Prospective cohort study. SETTING: Two tertiary academic centers. PATIENTS: We enrolled children younger than 18 years who were admitted to the PICU within 24 hours after insertion of a central venous catheter. We excluded children with a recently diagnosed thrombotic event or those anticipated to receive anticoagulation. Children with thrombosis diagnosed with surveillance ultrasonography on the day of enrollment were classified as having prevalent thrombosis. Those who developed catheter-related thrombosis thereafter were classified as having incident thrombosis. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We enrolled 85 children in the study. Once enrolled, we measured factor VIII activity with one-stage clotting assay and determined G value with thromboelastography. Of those enrolled, 25 had incident and 12 had prevalent thromboses. The odds ratio for incident thrombosis per SD increase in factor VIII activity was 1.98 (95% CI, 1.10-3.55). The area under the receiver operating characteristic curve was 0.66 (95% CI, 0.52-0.79). At factor VIII activity more than 100 IU/dL, which was the optimal threshold identified using Youden index, sensitivity and specificity were 92.0% and 41.3%, respectively. The association between factor VIII activity and incident thrombosis remained significant after adjusting for important clinical predictors of thrombosis (odds ratio, 1.93; 95% CI, 1.10-3.39). G value was associated with prevalent but not with incident thrombosis. CONCLUSION: Factor VIII activity may be used to stratify critically ill children based on their risk for catheter-related thrombosis.