1457. Epidemiology of Human Herpesvirus-6 Meningoencephalitis in Los Angeles County, 2016-2020

Background

Human herpesvirus 6 (HHV-6) is ubiquitous and a known central nervous system (CNS) pathogen. However, HHV-6 in cerebrospinal fluid (CSF) without clinical findings of meningoencephalitis (ME) may not represent true infection, but rather, asymptomatic viral reactivation, chromosomal integration, or latent activation. With the introduction in 2015 of a rapid polymerase chain reaction (PCR) multiplex panel that simultaneously tests for 14 CNS pathogens, reports of HHV-6 PCR positive ME have increased. We sought to understand the epidemiology of HHV-6 ME by evaluating reported cases in Los Angeles County (LAC) between 2016-2020.

Methods

ME is a reportable condition in LAC. We reviewed clinical, laboratory, and radiologic data for all HHV-6 PCR positive cases reported in LAC between 2016-2020. We developed case classification categories, “unlikely,” “possible,” and “likely”, based on symptoms, CSF profile, and alternative diagnoses (see Table 1).

Results

A total of 67 HHV-6 ME cases were reported (see Table 2). Reports increased over time, with one in 2016, 12 in 2017, 17 in 2018, 20 in 2019, and 17 in 2020. Median age was 9 months (range 0d-78y), and 47 (70%) were < three years old. Forty-four (66%) were male. Six (9%) were immunocompromised, including one hematopoietic stem cell transplant recipient. Nineteen (28%) had abnormal CSF, and eight (12%) received therapy for HHV-6.

Five cases (7%) were classified as “likely” HHV-6 ME, 12 (18%) “possible,” and 50 (75%) “unlikely”. The “likely” cases ranged in age from 7 months to 12 years old, and none were immunocompromised. One received antiviral therapy and was discharged to a rehabilitation facility, the other four were discharged home with full recovery.

Conclusion

The significance of HHV-6 in CSF remains challenging to determine both clinically and epidemiologically. In the setting of increased testing, increasing detection of HHV-6 in CSF may not reflect increasing rates of HHV-6 ME. The majority of reported HHV-6 ME cases were “unlikely” based on our classification. Classifying cases with alternative diagnoses as ‘unlikely” may miss cases with multiple true infections, particularly in the immunocompromised. It is important to consider clinical presentation, CSF profile and other diagnoses to understand the true burden of HHV-6 ME.

Disclosures

All Authors: No reported disclosures.

Industry Sectors Highly Affected by Worksite Outbreaks of Coronavirus Disease, Los Angeles County, California, USA, March 19-September 30, 2020

Worksites with on-site operations have experienced coronavirus disease (COVID-19) outbreaks. We analyzed data for 698 nonresidential, nonhealthcare worksite COVID-19 outbreaks investigated in Los Angeles County, California, USA, during March 19, 2020‒September 30, 2020, by using North American Industry Classification System sectors and subsectors. Nearly 60% of these outbreaks occurred in 3 sectors: manufacturing (n = 184, 26.4%), retail trade (n = 137, 19.6%), and transportation and warehousing (n = 73, 10.5%). The largest number of outbreaks and largest number and highest incidence rate of outbreak-associated cases occurred in manufacturing. Furthermore, 7 of the 10 industry subsectors with the highest incidence rates were within manufacturing. Approximately 70% of outbreak-associated case-patients reported Hispanic ethnicity. Facilities employing more on-site staff had larger and longer outbreaks. Identification of highly affected industry sectors and subsectors is necessary for targeted public health planning, outreach, and response, including ensuring vaccine access, to reduce burden of COVID-19 in vulnerable workers.

Varicella Vaccine Effectiveness in Preventing Community Transmission in the 2-Dose Era

OBJECTIVES

We examined overall and incremental effectiveness of 2-dose varicella vaccination in preventing community transmission of varicella among children aged 4 to 18 years in 2 active surveillance sites. One-dose varicella vaccine effectiveness (VE) was examined in those aged 1 to 18 years.

METHODS

From May 2009 through June 2011, varicella cases identified during active surveillance in Antelope Valley, CA and Philadelphia, PA were enrolled into a matched case-control study. Matched controls within 2 years of the patient's age were selected from immunization registries. A standardized questionnaire was administered to participants' parents, and varicella vaccination history was obtained from health care provider, immunization registry, or parent records. We used conditional logistic regression to estimate varicella VE against clinically diagnosed and laboratory-confirmed varicella.

RESULTS

A total of 125 clinically diagnosed varicella cases and 408 matched controls were enrolled. Twenty-nine cases were laboratory confirmed. One-dose VE (1-dose versus unvaccinated) was 75.6% (95% confidence interval [CI], 38.7%-90.3%) in preventing any clinically diagnosed varicella and 78.1% (95% CI, 12.7%-94.5%) against moderate or severe, clinically diagnosed disease (≥50 lesions). Among subjects aged ≥4 years, 2-dose VE (2-dose versus unvaccinated) was 93.6% (95% CI, 75.6%-98.3%) against any varicella and 97.9% (95% CI, 83.0%-99.7%) against moderate or severe varicella. Incremental effectiveness (2-dose versus 1-dose) was 87.5% against clinically diagnosed varicella and 97.3% against laboratory-confirmed varicella.

CONCLUSIONS

Two-dose varicella vaccination offered better protection against varicella from community transmission among school-aged children compared with 1-dose vaccination.