A narrative review of norovirus epidemiology, biology, and challenges to vaccine development.

Norovirus is a leading cause of acute gastroenteritis (AGE) globally. AGE resulting from norovirus causes significant morbidity and mortality in countries of all income levels, particularly among young children and older adults. Prevention of norovirus AGE represents a unique challenge as the virus is genetically diverse with multiple genogroups and genotypes cocirculating globally and causing disease in humans. Variants of the GII.4 genotype are typically the most common genotype, and other genotypes cause varying amounts of disease year-to-year, with GII.2, GII.3, and GII.6 most prevalent in recent years. Noroviruses are primarily transmitted via the fecal-oral route and only a very small number of virions are required for infection, which makes outbreaks of norovirus extremely difficult to control when they occur. Settings like long-term care facilities, daycares, and hospitals are at high risk of outbreaks and can have very high attack rates resulting in substantial costs and disease burden. Severe cases of norovirus AGE are most common in vulnerable patient populations, such as infants, the elderly, and immunocompromised individuals, with available treatments limited to rehydration therapies and supportive care. To date, there are no FDA-approved norovirus vaccines; however, several candidates are currently in development. Given the substantial human and economic burden associated with norovirus AGE, a vaccine to prevent morbidity and mortality and protect vulnerable populations could have a significant impact on global public health.

Prevalence of Diagnosed Genital Herpes and Antiviral Treatment in the United States.

BACKGROUND: Genital herpes is a common sexually transmitted infection caused by the herpes simplex virus. Contemporary United States (US) population-based epidemiologic data on genital herpes are limited. This study aimed to provide nationally representative estimates of genital herpes prevalence and treatment using a large US health insurance claims database. METHODS: This observational cohort study used administrative claims data from HealthVerity. Crude and age- and sex-standardized prevalence rates of genital herpes and recurrent genital herpes were calculated for the years 2019 to 2021. The distribution of patients with prevalent genital herpes who received episodic or suppressive antiviral therapy was also estimated. RESULTS: From 2019 to 2021, the standardized prevalence of genital herpes and recurrent genital herpes ranged from 236 to 280 cases per 100,000 person-years and 81 to 98 cases per 100,000 person-years, respectively. The prevalence of genital herpes was highest among those aged 25-29 years (prevalence range: 497 to 582), female patients (prevalence range: 348 to 404), and those with a history of HIV infection (prevalence range: 1608 to 2080). The prevalence of recurrent genital herpes was also highest in these groups. From 2019 to 2021, two-thirds of patients (65% to 68%) with prevalent genital herpes received antiviral medications; the majority received episodic therapy (80%) rather than suppressive therapy (20%). CONCLUSIONS: The burden of genital herpes and recurrent genital herpes in the US is substantial, with the highest rates observed in young adults, women, and immunocompromised individuals. About two-thirds receive antiviral treatment each year.

Incidence of Herpes Zoster and Postherpetic Neuralgia and Herpes Zoster Vaccination Uptake in a US Administrative Claims Database.

Background: The objective of this study was to estimate the annual incidence rates of herpes zoster (HZ) and postherpetic neuralgia (PHN) among individuals aged ≥19 years and the proportion who received HZ vaccination among those aged ≥50 years. Methods: This observational cohort study was conducted with administrative claims data from HealthVerity and included insured individuals across the US. Crude and US age- and sex-standardized incidence rates of HZ and PHN were calculated from 1 January 2019 to 31 May 2022 by calendar year in persons aged ≥19 years. Outcomes were defined as ≥1 ICD-10 diagnosis code for HZ or PHN. Analyses were stratified by age, sex, and immunocompromised status. Among those aged ≥50 years, the proportion who received 1 or 2 doses of recombinant zoster vaccine (Shingrix) or 1 dose of Zostavax was calculated. Results: Standardized annual incidence rates from 2019 to 2021 were 542 to 685 per 100 000 person-years for HZ and 35 to 38 per 100 000 person-years for PHN. Rates were highest among females, older adults, and individuals who were immunocompromised. From 1 January 2019 to 31 May 2022, 4.3% and 9.0% of persons aged ≥50 years received 1 and 2 doses of Shingrix, respectively, and 0.2% received 1 dose of Zostavax. Conclusions: In this US claims database analysis, HZ and PHN were more frequent among older adults, females, and individuals who were immunocompromised. Between 1 January 2019 and 31 May 2022, 9% of persons aged ≥50 years received 2 doses of the Shingrix vaccine. Greater efforts are needed to increase vaccine uptake against HZ, especially for those at highest risk.

Increased Risk of Venous Thromboembolism in Patients With Amyotrophic Lateral Sclerosis: Results From a US Insurance Claims Database Study.

Background and Objectives: Reduced mobility in patients with amyotrophic lateral sclerosis (ALS) is hypothesized to increase the risk of venous thromboembolism (VTE). A few small, single-center studies have investigated the risk of VTE in patients with ALS. Given the high morbidity and mortality associated with VTE, further understanding of the risk in patients with ALS may inform clinical care. The objective of this study was to investigate the incidence of VTE in patients with ALS compared with controls without ALS. Methods: Patients were identified from a US health insurance claims database, Optum's deidentified Clinformatics Data Mart Database, between 2004 and 2019. ALS cases were defined as patients aged 18 years or older with (1) 2 or more ALS claims at least 27 days apart including at least 1 claim from a neurologist visit or (2) 1 or more ALS claims and a prescription for riluzole or edaravone. Each ALS case was matched on age and sex to 5 controls without ALS. VTE was defined as at least 1 claim for VTE and at least 1 anticoagulant prescription or VTE-related procedure within 7 days before and 30 days after a VTE claim date. Incidence rates were reported per 1,000 person-years. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using the Cox proportional hazards model. Results: Among 4,205 ALS cases and 21,025 controls, incident VTE occurred in 132 ALS cases (3.1%) and 244 controls (1.2%). Incidence rates of VTE were 19.9 per 1,000 person-years (95% CI 16.7-23.6) in ALS cases compared with 6.0 per 1,000 person-years (95% CI 5.0-7.1) in controls. ALS cases were about 3 times more likely to develop VTE (HR 3.3, 95% CI 2.6-4.0), with similar results among men and women. The median time to first VTE was 10 months from the initial ALS claim in ALS cases. Discussion: Consistent with previous smaller studies, a higher incidence rate of VTE was observed in a large sample of patients with ALS from across the United States, as compared to matched controls. The markedly increased risk underscores the importance of preventive efforts and careful monitoring for VTE in patients with ALS and may have implications for the management of ALS.

Examining Real-World Adherence to Nusinersen for the Treatment of Spinal Muscular Atrophy Using Two Large US Data Sources.

INTRODUCTION: Spinal muscular atrophy (SMA) is a rare neuromuscular disease characterized by progressive muscular atrophy and weakness. Nusinersen was the first treatment approved for SMA. Per the US label, the nusinersen administration schedule consists of three loading doses at 14-day intervals, a fourth loading dose 30 days later, and maintenance doses every 4 months thereafter. Using two large US databases, we evaluated real-world adherence to nusinersen with its unique dosing schedule among generalizable populations of patients with SMA. METHODS: Patients with SMA treated with nusinersen, likely to have complete information on date of treatment initiation, were identified in the Optum® de-identified electronic health records (EHR) database (7/2017-9/2019), and in the Merative™ MarketScan® Research Databases from commercial (1/2017-6/2020) and Medicaid claims (1/2017-12/2019). Baseline demographics, number of nusinersen administrations on time, and distribution of inter-dose intervals were summarized. RESULTS: Totals of 67 and 291 patients were identified in the EHR and claims databases, respectively. Most nusinersen doses were received on time (93.9% EHR, 80.5% claims). Adherence was higher during the maintenance phase (90.6%) than the loading phase (71.1%) in the claims analysis, in contrast with the EHR analysis (95.5% and 92.6%, respectively), suggesting that not all loading doses of nusinersen may be accurately captured in claims. Inter-dose intervals captured in both databases aligned with the expected dosing schedule. CONCLUSION: Most nusinersen doses were received on time, consistent with the recommended schedule. Our findings also highlight the importance of careful methodological approaches when using real-world administrative databases for evaluation of nusinersen treatment patterns.

Adherence to medicines in the real world is important for patients with chronic disease to see long-term benefits of treatment. This study shows the importance and challenges of measuring adherence using real-world administrative data sources. This is especially important for drugs given through lumbar puncture with unique dosing schedules, such as nusinersen for the treatment of spinal muscular atrophy. In this study, most patients with spinal muscular atrophy received their nusinersen doses on time.

Comparative All-Cause Mortality Among a Large Population of Patients with Spinal Muscular Atrophy Versus Matched Controls.

INTRODUCTION: There is little information about survival of spinal muscular atrophy (SMA) patients into adulthood, in particular from population-based samples. We estimated and compared age-specific, all-cause mortality rates in patients with SMA and matched controls in a large, retrospective cohort study using electronic health records (EHRs) from the pre-treatment era. METHODS: The US Optum® de-identified EHR database contains EHRs for ~ 104 million persons (study period: January 1, 2007-December 22, 2016). SMA cases were identified by one or more International Classification of Diseases, Ninth/Tenth Edition codes for SMA. Controls with no SMA diagnosis code were matched 10:1 to SMA cases based on birth year, gender, and first diagnostic code date. For both groups, ≥ 1 month of observation and (if deceased) a valid date of death were required for inclusion. Age-specific mortality rates per person-year (PY) and hazard ratios were calculated. RESULTS: Five thousand one hundred seventy-nine SMA cases and 51,152 controls were analyzed. The overall hazard ratio comparing cases with controls was 1.76 (95% CI 1.63-1.90). In patients with SMA type III diagnostic codes only, the all-age mortality rate was 1059/100,000 PYs in cases and 603/100,000 PYs in controls. In older age groups (13-20, 21-30, 31-40, 41-50, 51-60, and > 60 years), age-specific mortality rates for cases consistently exceeded those of controls. Limitations of this study included the inability to confirm the SMA diagnosis or SMA type by genetic or clinical confirmation. CONCLUSION: Patients with SMA of all ages, including adults and type III patients, had a higher all-cause mortality rate as compared to age-matched controls during the pre-treatment era.

Clinical Features of Patients With Progressive Supranuclear Palsy in an US Insurance Claims Database.

Background: Progressive supranuclear palsy is a rare neurodegenerative movement disorder and little is known about its epidemiology. Objective: Estimate age-adjusted prevalence of progressive supranuclear palsy and describe antecedent diagnoses and progressive supranuclear palsy patient features in the 5 years before first diagnostic code. Methods: In a nested case-control study in the IBM MarketScan Commercial and Medicare Supplemental Databases, a large set of US insurance databases containing medical service and prescription drug claims from employer-based commercial and Medicare supplemental health insurance plans, progressive supranuclear palsy cases (identified via International Statistical Classification of Diseases 9th/10th revision codes) and controls were included if enrollment was ≥1 month in the study period (October 1, 2015-October 31, 2017). Two controls with no diagnosis codes for PSP were matched to cases on birth year, sex, enrollment time in the database, and pharmacy benefit eligibility. Controls were assigned a randomly selected index date from their eligibility period. Prevalence of progressive supranuclear palsy was estimated in 2016 among patients with ≥1 month of continuous enrollment in that year. Prevalence ratios for comorbidities (claim/diagnosis codes) were examined in the ≤ 5 years before index date (first progressive supranuclear palsy claim date). Results: Age-adjusted progressive supranuclear palsy prevalence was 2.95/100,000 in 2016. The most common diagnosis codes in cases vs. controls in the 5 years pre-index were gait abnormalities (79.3 vs. 21.8%), pain in joint (54.9 vs. 36.0%), Parkinson's disease (54.6 vs. 1.0%), fatigue (49.8 vs. 21.6%), and cerebrovascular disease (45.6 vs. 16.4%). Conclusions: In this large database analysis, based on preliminary analyses, the prevalence of diagnosed progressive supranuclear palsy was 2.95/100,000, which is lower than many prior studies. Typical symptoms suggestive of progressive supranuclear palsy were present before index date, indicating a potential delay in time to diagnosis. The identification of diagnostic codes for clinical features of progressive supranuclear palsy that occurred before index date may be used to develop predictive models to identify potential progressive supranuclear palsy patients earlier in their disease course.

The incidence of hydrocephalus among patients with and without spinal muscular atrophy (SMA): Results from a US electronic health records study.

BACKGROUND: The incidence of hydrocephalus in the spinal muscular atrophy (SMA) population relative to the general population is currently unknown. Since the approval of nusinersen, an intrathecally administered drug for SMA, a small number of hydrocephalus cases among nusinersen users have been reported. Currently, the incidence of hydrocephalus in untreated SMA patients is not available, thereby making it difficult to determine if hydrocephalus is a side effect of nusinersen or part of SMA's natural history. This retrospective, matched cohort study used electronic health records (EHRs) to estimate and compare the incidence of hydrocephalus in both SMA patients and matched non-SMA controls in the time period prior to the approval of nusinersen. METHODS: The U.S. Optum® de-identified EHR database contains records for approximately 100 million persons. The current study period spanned January 1, 2007-December 22, 2016. Patients with SMA were identified by one or more International Classification of Diseases (ICD)-9 and/or ICD-10 codes for SMA appearing as primary, admission, or discharge diagnoses, without a pregnancy diagnostic code in the 1-year time before and after the first occurrence of SMA. The first occurrence of SMA defined the index date and non-SMA controls were matched to cases. Incident cases of hydrocephalus were identified with one or more ICD-9 and/or ICD-10 code for any type of hydrocephalus following the index date. Hydrocephalus incidence rates per person-months and the incidence rate ratio comparing SMA cases with non-SMA controls were calculated. RESULTS: There were 5354 SMA cases and an equal number of matched non-SMA controls. Incident hydrocephalus events were identified in 42 SMA cases and 9 non-SMA controls. Hydrocephalus incidence rates per 100,000 person-months were 15.5 (95% CI: 11.2-20.9) among SMA cases and 3.3 (95% CI: 1.5-6.3) among non-SMA controls. The incidence rate ratio was 4.7 (95% CI: 2.4-10.2). CONCLUSIONS: Based on this retrospective analysis utilizing US EHR data, SMA patients had an approximately fourfold increased risk of hydrocephalus compared with non-SMA controls in the era preceding nusinersen treatment. This study may assist in properly evaluating adverse events in nusinersen-treated SMA patients.

A case-control analysis of smoking and breast cancer in African American women: findings from the AMBER Consortium.

Recent population studies suggest a role of smoking in the etiology of breast cancer, but few have been conducted among African American women. In a collaborative project of four large studies, we examined associations between smoking measures and breast cancer risk by menopause and hormone receptor status [estrogen receptor-positive (ER+), ER-negative (ER-) and triple-negative (ER-, PR-, HER2-)]. The study included 5791 African American women with breast cancer and 17376 African American controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated in multivariable logistic regression analysis with adjustment for study and risk factors. Results differed by menopausal status. Among postmenopausal women, positive associations were observed for long duration and greater pack-years of smoking: relative to never smoking, fully adjusted ORs were 1.14 (95% CI: 1.03-1.26) for duration ≥20 years and 1.16 (95% CI: 1.01-1.33) for ≥20 pack-years. By contrast, inverse associations were observed among premenopausal women, with ORs of 0.80 (95% CI: 0.68-95) for current smoking and 0.81 (95% CI: 0.69-0.96) for former smoking, without trends by duration. Associations among postmenopausal women were somewhat stronger for ER+ breast cancer. The findings suggest that the relation of cigarette smoking to breast cancer risk in African American women may vary by menopausal status and breast cancer subtype.

Postmenopausal Female Hormone Use and Estrogen Receptor-Positive and -Negative Breast Cancer in African American Women.

BACKGROUND: Use of estrogen with progestin (combination therapy) is associated with increased incidence of estrogen receptor-positive (ER+) breast cancer in observational studies and randomized trials among postmenopausal white women. Whether this is also the case among African American women is not established. METHODS: Using data from the AMBER consortium collected from 1993 to 2013, we assessed use of estrogen alone and of combination therapy in relation to ER+ and ER-negative (ER-) breast cancer risk in postmenopausal African American women, based on 1132 ER+ case patients, 512 ER- case patients, and 6693 control patients. Odds ratios (ORs) and confidence intervals (CIs) were estimated using multinomial logistic regression with control for breast cancer risk factors. RESULTS: Forty-seven percent of control patients had used estrogen alone, combination therapy, or both. The odds ratio for ER+ breast cancer associated with combination use, relative to never use of either estrogen alone or combination therapy, was 1.50 (95% CI = 1.25 to 1.79). The increase was greater for recent (OR = 1.55, 95% CI = 1.21 to 1.99) and long-term use (OR = 1.75, 95% CI = 1.13 to 2.73) and among nonobese women (OR = 1.91, 95% CI = 1.29 to 2.83). Breast cancer risk was increased regardless of the interval between onset of menopause and initiation of combination use (OR = 1.43, 95% CI = 1.11 to 1.85, for <5 year interval; OR = 1.78, 95% CI = 1.34 to 2.37, for ≥5 year interval). Combination use was not associated with risk of ER- breast cancer, and use of estrogen alone was not associated with risk of either ER+ or ER- breast cancer. CONCLUSION: Use of estrogen with progestin increases risk of ER+ breast cancer in African American women. A decrease in use would be expected to reduce the number of ER+ cancers.

Female Autism Phenotypes Investigated at Different Levels of Language and Developmental Abilities.

This study investigated the differences in clinical symptoms between females and males with autism spectrum disorder (ASD) across three verbal ability groups (nonverbal, phrase and fluent speech), based on which Autism Diagnostic Observation Schedule module was administered to 5723 individuals in four research datasets. In the Simons Simplex Collection and Autism Treatment Network, females with ASD and phrase or fluent speech had lower cognitive, adaptive, and social abilities than males. In the Autism Genetics Resource Exchange and the Autism Consortium, females with phrase or fluent speech had similar or better adaptive and social abilities than males. Females who were nonverbal had similar cognitive, adaptive, and social abilities as males. Population-based longitudinal studies of verbally fluent females with ASD are needed.

Parity, lactation, and breast cancer subtypes in African American women: results from the AMBER Consortium.

BACKGROUND: African American (AA) women have a disproportionately high incidence of estrogen receptor-negative (ER-) breast cancer, a subtype with a largely unexplained etiology. Because childbearing patterns also differ by race/ethnicity, with higher parity and a lower prevalence of lactation in AA women, we investigated the relation of parity and lactation to risk of specific breast cancer subtypes. METHODS: Questionnaire data from two cohort and two case-control studies of breast cancer in AA women were combined and harmonized. Case patients were classified as ER+ (n = 2446), ER- (n = 1252), or triple negative (ER-, PR-, HER2-; n = 567) based on pathology data; there were 14180 control patients. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated in polytomous logistic regression analysis with adjustment for study, age, reproductive and other risk factors. RESULTS: ORs for parity relative to nulliparity was 0.92 (95% CI = 0.81 to 1.03) for ER+, 1.33 (95% CI = 1.11 to 1.59) for ER-, and 1.37 (95% CI = 1.06 to 1.70) for triple-negative breast cancer. Lactation was associated with a reduced risk of ER- (OR = 0.81, 95% CI = 0.69 to 0.95) but not ER+ cancer. ER- cancer risk increased with each additional birth in women who had not breastfed, with an OR of 1.68 (95% CI = 1.15 to 2.44) for 4 or more births relative to one birth with lactation. CONCLUSIONS: The findings suggest that parous women who have not breastfed are at increased risk of ER- and triple-negative breast cancer. Promotion of lactation may be an effective tool for reducing occurrence of the subtypes that contribute disproportionately to breast cancer mortality.

The association between epilepsy and autism symptoms and maladaptive behaviors in children with autism spectrum disorder.

Epilepsy is common in children with autism spectrum disorder (ASD) but little is known about how seizures impact the autism phenotype. The association between epilepsy and autism symptoms and associated maladaptive behaviors was examined in 2,645 children with ASD, of whom 139 had epilepsy, from the Simons Simplex Collection. Children with ASD and epilepsy had significantly more autism symptoms and maladaptive behaviors than children without epilepsy. However, after adjusting for IQ, only hyperactivity symptoms remained significantly increased (13% higher) in the epilepsy group. Among children with ASD without co-occurring intellectual disability, children with epilepsy had significantly more irritability (20% higher) and hyperactivity (24% higher) symptoms. This is the largest study to date comparing the autism phenotype in children with ASD with and without epilepsy. Children with ASD and epilepsy showed greater impairment than children without epilepsy, which was mostly explained by the lower IQ of the epilepsy group. These findings have important clinical implications for patients with ASD.

Intellectual disability is associated with increased runs of homozygosity in simplex autism.

Intellectual disability (ID), often attributed to autosomal-recessive mutations, occurs in 40% of autism spectrum disorders (ASDs). For this reason, we conducted a genome-wide analysis of runs of homozygosity (ROH) in simplex ASD-affected families consisting of a proband diagnosed with ASD and at least one unaffected sibling. In these families, probands with an IQ ≤ 70 show more ROH than their unaffected siblings, whereas probands with an IQ > 70 do not show this excess. Although ASD is far more common in males than in females, the proportion of females increases with decreasing IQ. Our data do support an association between ROH burden and autism diagnosis in girls; however, we are not able to show that this effect is independent of low IQ. We have also discovered several autism candidate genes on the basis of finding (1) a single gene that is within an ROH interval and that is recurrent in autism or (2) a gene that is within an autism ROH block and that harbors a homozygous, rare deleterious variant upon analysis of exome-sequencing data. In summary, our data suggest a distinct genetic architecture for participants with autism and co-occurring intellectual disability and that this architecture could involve a role for recessively inherited loci for this autism subgroup.

Clinical characteristics of children with autism spectrum disorder and co-occurring epilepsy.

OBJECTIVES: To estimate the prevalence of epilepsy in children with Autism Spectrum Disorder (ASD) and to determine the demographic and clinical characteristics of children with ASD and epilepsy in a large patient population. METHODS: Cross-sectional study using four samples of children with ASD for a total of 5,815 participants with ASD. The prevalence of epilepsy was estimated from a population-based sample. Children with and without epilepsy were compared on demographic and clinical characteristics. Multivariate logistic regression was used to examine the association between demographic and clinical characteristics and epilepsy. RESULTS: The average prevalence of epilepsy in children with ASD 2-17 years was 12.5%; among children aged 13 years and older, 26% had epilepsy. Epilepsy was associated with older age, lower cognitive ability, poorer adaptive and language functioning, a history of developmental regression and more severe ASD symptoms. The association between epilepsy and the majority of these characteristics appears to be driven by the lower IQ of participants with epilepsy. In a multivariate regression model, only age and cognitive ability were independently associated with epilepsy. Children age 10 or older had 2.35 times the odds of being diagnosed with epilepsy (p<.001) and for a one standard deviation increase in IQ, the odds of having epilepsy decreased by 47% (p<.001). CONCLUSION: This is among the largest studies to date of patients with ASD and co-occurring epilepsy. Based on a representative sample of children with ASD, the average prevalence of epilepsy is approximately 12% and reaches 26% by adolescence. Independent associations were found between epilepsy and older age and lower cognitive ability. Other risk factors, such as poor language and developmental regression, are not associated with epilepsy after controlling for IQ. These findings can help guide prognosis and alert clinicians to patients with ASD who are at increased risk for epilepsy.

Disease-specific alterations in glutamatergic neurotransmission on inhibitory interneurons in the prefrontal cortex in schizophrenia.

Glutamatergic modulation of inhibitory interneurons plays a crucial role in shaping the flow of information in the cerebral cortex. In a cohort of postmortem human brains from schizophrenia (n=20), bipolar disorder (n=20) and normal control (n=20) subjects, we colocalized the mRNA for the N-methyl-d-aspartate (NMDA) receptor NR2A subunit, labeled with [35S], and the mRNA for the gamma-aminobutyric acid (GABA) synthesizing enzyme glutamic acid decarboxylase (GAD)67, labeled with digoxigenin. We found that the density of GAD67+ neurons in layers 2-5 of the prefrontal cortex was decreased by 27-36% in both schizophrenia and bipolar disorder. In addition, the density of the GAD67+/NR2A+ neurons was decreased by 57% and 49% in layers 3 and 4, respectively, in schizophrenia, but it was unchanged in bipolar disorder. These findings raise the possibility that glutamatergic innervation of inhibitory interneurons via the NMDA receptor in the prefrontal cortex may be selectively altered in schizophrenia.

Serological cross-reactivities between antibodies to simian virus 40, BK virus, and JC virus assessed by virus-like-particle-based enzyme immunoassays.

Enzyme immunoassays (EIAs) for detection of serum antibodies to simian virus 40 (SV40), BK virus (BKV), and JC virus (JCV) were developed by using virus-like-particles (VLPs) produced in insect cells from recombinant baculoviruses expressing the VP1 protein of the respective virus. Rhesus macaque sera with neutralizing antibodies to SV40 showed a high level of reactivity in the SV40 VLP-based EIA, and these sera also showed lower levels of reactivity in the BKV and JCV VLP-based EIAs. Rhesus macaque sera negative for neutralizing antibodies to SV40 were negative in all three EIAs. Competitive binding assays showed that SV40 VLPs inhibited BKV reactivity. In rhesus macaque sera, high optical density (OD) values for antibodies to SV40 VLPs were correlated with high OD values for antibodies to BKV but not with high OD values for antibodies to JCV VLPs. Human sera with neutralizing antibodies to SV40 were more reactive to SV40 VLPs than human sera without neutralizing antibodies to SV40. The greater SV40 reactivities of human sera were correlated with greater reactivities to BKV VLPs but not JCV VLPs. These data suggest that cross-reactivity with BKV antibodies may account for part of the low-level SV40 reactivity seen in human sera. With their greater versatility and their suitability for large-scale testing, the VLP-based EIAs for SV40, BKV, and JCV are likely to contribute to a better understanding of the biology of these viruses.