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Local vector control and public health agencies in California use the California Mosquito-Borne Virus Surveillance and Response Plan to monitor and evaluate West Nile virus (WNV) activity and guide responses to reduce the burden of WNV disease. All available data from environmental surveillance, such as the abundance and WNV infection rates in Culex tarsalis and the Culex pipiens complex mosquitoes, the numbers of dead birds, seroconversions in sentinel chickens, and ambient air temperatures, are fed into a formula to estimate the risk level and associated risk of human infections. In many other areas of the US, the vector index, based only on vector mosquito abundance and infection rates, is used by vector control programs to estimate the risk of human WNV transmission. We built models to determine the association between risk level and the number of reported symptomatic human disease cases with onset in the following three weeks to identify the essential components of the risk level and to compare California’s risk estimates to vector index. Risk level calculations based on Cx . tarsalis and Cx . pipiens complex levels were significantly associated with increased human risk, particularly when accounting for vector control area and population, and were better predictors than using vector index. Including all potential environmental components created an effective tool to estimate the risk of WNV transmission to humans in California.

Monkeypox virus (MPXV) infection typically lasts 14-28 days. Prolonged MPXV infection, in which symptoms or test positivity last >28 days, has been documented but not fully characterized. We used the California Department of Public Health (California, USA) mpox registry to compare prolonged (>28 days) and nonprolonged (<28 days) mpox cases by demographics, HIV status, and JYNNEOS vaccination status. Of 6,469 cases, 82 (1.3%) were prolonged. Persons with prolonged MPXV infections were more likely to be Black or African American (prolonged, 20.7%, vs. nonprolonged, 11.6%) and to have HIV (prolonged, 61.0%, vs. nonprolonged, 39.9%). Among persons with HIV, prolonged infections were more likely among those with lower (<200) CD4 counts (prolonged, 10.0%, vs. nonprolonged, 3.9%) or not engaged in HIV care (prolonged, 46.0%, vs. nonprolonged, 18.1%). No prolonged infections occurred in persons who received 2 JYNNEOS vaccine doses. Groups disproportionately affected by prolonged mpox should be prioritized for mpox vaccine education and outreach.

The JYNNEOS modified vaccinia virus Ankara vaccine is effective in preventing clade IIb mpox disease. However, vaccine effects on mpox severity are poorly understood. We aimed to assess associations between reported clinical characteristics and vaccination status among individuals with laboratory-confirmed mpox. We conducted a case–control study using data collected from public health surveillance interviews of people with mpox in California. Eligible participants for primary analyses were men who were cisgender and participated in telephone interviews with complete responses recorded about anatomical sites where they had lesions. We estimated JYNNEOS vaccine effectiveness against progression to disease involving disseminated lesions via the adjusted odds ratio of vaccination, comparing participants who reported lesions disseminated across multiple anatomical regions (cases) with participants who reported lesions contained to a single anatomical region (controls). We used the same case–control framework to estimate vaccine effectiveness against progression to hospitalisation and prodromal symptoms. Men who were cisgender represented 5763 (94·3%) of 6112 people reported to have laboratory-confrimed mpox in California from May 12, 2022, to Dec 31, 2023, among whom, 4609 (79·9%) met eligibility criteria and were included in primary analyses. Of 4609 participants, 1566 (34·0%) were classified as controls and 3043 (66·0%) were classified as cases. Among 3043 cases, 114 (3·7%) received pre-exposure vaccination and 214 (7·0%) received post-exposure vaccination only. Among 1566 controls, 285 (18·2%) received pre-exposure vaccination and 146 (9·3%) received post-exposure vaccination only. For pre-exposure vaccination, vaccine effectiveness against progression was 58·8% (95% CI 50·3–65·9); for post-exposure vaccination, vaccine effectiveness against progression was 15·9% (3·3–26·8). Pre-exposure vaccine effectiveness against progression was 66·6% (56·8–74·2) among people negative for HIV and 44·8% (27·5–58·0) for those with HIV. Pre-exposure vaccination was also associated with protection against progression to severe illness necessitating hospitalisation (85·4% [95% CI 54·3–95·3]), and with reduced odds for fever, chills, and lymphadenopathy. Among men who were cisgender with mpox, pre-exposure vaccination with JYNNEOS was associated with less severe illness. Awareness of an attenuated disease phenotype involving localised lesions without accompanying prodromal symptoms is needed to ensure accurate diagnosis of mpox in previously vaccinated individuals. The California Department of Public Health and the US National Institutes of Health.

The spread of Aedes aegypti in California and other regions of the U.S. has increased the need to understand the potential for local chains of Ae. aegypti-borne virus transmission, particularly in arid regions where the ecology of these mosquitoes is less understood. For public health and vector control programs, it is helpful to know whether variation in risk of local transmission can be attributed to socio-demographic factors that could help to target surveillance and control programs. Socio-demographic factors have been shown to influence transmission risk of dengue virus outside the U.S. by modifying biting rates and vector abundance. In regions of the U.S. where Ae. aegypti have recently invaded and where residential areas are structured differently than those in the tropics where Ae. aegypti are endemic, it is unclear how socio-demographic factors modify the abundance of Ae. aegypti populations. Understanding heterogeneities among households in Ae. aegypti abundance will provide a better understanding of local vectorial capacity and is an important component of understanding risk of local Ae. aegypti-borne virus transmission. We conducted a cross-sectional study in Los Angeles County, California during summer 2017 to understand the causes of variation in relative abundance of Ae. aegypti among households. We surveyed 161 houses, representing a wide range of incomes. Surveys consisted of systematic adult mosquito collections, inspections of households and properties, and administration of a questionnaire in English or Spanish. Adult Ae. aegypti were detected at 72% of households overall and were found indoors at 12% of households. An average of 3.1 Ae. aegypti were collected per household. Ae. aegypti abundance outdoors was higher in lower-income neighborhoods and around older households with larger outdoor areas, greater densities of containers with standing water, less frequent yard maintenance, and greater air-conditioner use. We also found that Ae. aegypti abundance indoors was higher in households that had less window and door screening, less air-conditioner usage, more potted plants indoors, more rain-exposed containers around the home, and lower neighborhood human population densities. Our results indicate that, in the areas of southern California studied, there are behavioral and socio-demographic determinants of Ae. aegypti abundance, and that low-income households could be at higher risk for exposure to Ae. aegypti biting and potentially greater risk for Zika, dengue, and chikungunya virus transmission if a local outbreak were to occur.

The California Arbovirus Surveillance Program was initiated over 50 years ago to track endemic encephalitides and was enhanced in 2000 to include West Nile virus (WNV) infections in humans, mosquitoes, sentinel chickens, dead birds and horses. This comprehensive statewide program is a function of strong partnerships among the California Department of Public Health (CDPH), the University of California, and local vector control and public health agencies. This manuscript summarizes WNV surveillance data in California since WNV was first detected in 2003 in southern California. From 2003 through 2018, 6,909 human cases of WNV disease, inclusive of 326 deaths, were reported to CDPH, as well as 730 asymptomatic WNV infections identified during screening of blood and organ donors. Of these, 4,073 (59.0%) were reported as West Nile neuroinvasive disease. California’s WNV disease burden comprised 15% of all cases that were reported to the U.S. Centers for Disease Control and Prevention during this time, more than any other state. Additionally, 1,299 equine WNV cases were identified, along with detections of WNV in 23,322 dead birds, 31,695 mosquito pools, and 7,340 sentinel chickens. Annual enzootic detection of WNV typically preceded detection in humans and prompted enhanced intervention to reduce the risk of WNV transmission. Peak WNV activity occurred from July through October in the Central Valley and southern California. Less than five percent of WNV activity occurred in other regions of the state or outside of this time. WNV continues to be a major threat to public and wild avian health in California, particularly in southern California and the Central Valley during summer and early fall months. Local and state public health partners must continue statewide human and mosquito surveillance and facilitate effective mosquito control and bite prevention measures.

St. Louis encephalitis virus (SLEV) is an endemic flavivirus in the western and southeastern United States, including California. From 1938 to 2003, the virus was detected annually in California, but after West Nile virus (WNV) arrived in 2003, SLEV was not detected again until it re-emerged in Riverside County in 2015. The re-emerging virus in California and other areas of the western US is SLEV genotype III, which previously had been detected only in Argentina, suggesting a South American origin. This study describes SLEV activity in California since its re-emergence in 2015 and compares it to WNV activity during the same period. From 2015 to 2020, SLEV was detected in 1,650 mosquito pools and 26 sentinel chickens, whereas WNV was detected concurrently in 18,108 mosquito pools and 1,542 sentinel chickens from the same samples. There were 24 reported human infections of SLEV in 10 California counties, including two fatalities (case fatality rate: 8%), compared to 2,469 reported human infections of WNV from 43 California counties, with 143 fatalities (case fatality rate: 6%). From 2015 through 2020, SLEV was detected in 17 (29%) of California’s 58 counties, while WNV was detected in 54 (93%). Although mosquitoes and sentinel chickens have been tested routinely for arboviruses in California for over fifty years, surveillance has not been uniform throughout the state. Of note, since 2005 there has been a steady decline in the use of sentinel chickens among vector control agencies, potentially contributing to gaps in SLEV surveillance. The incidence of SLEV disease in California may have been underestimated because human surveillance for SLEV relied on an environmental detection to trigger SLEV patient screening and mosquito surveillance effort is spatially variable. In addition, human diagnostic testing usually relies on changes in host antibodies and SLEV infection can be indistinguishable from infection with other flaviviruses such as WNV, which is more prevalent.

In December 2014, during the height of the Ebola virus disease (EVD) epidemic in West Africa, we wrote, “EVD is only the beginning and only one disease; even if we are to control the current epidemic, the future introduction of this and other highly contagious and virulent microbes to and from global slums is inevitable” [1].Fast forward to late 2015: another epidemic of another virus-Zika-together with its major neurological complication-microcephaly-explodes in Brazil. Again, as with the EVD epidemic, the world’s attention is focused on issues such as where the virus originated, the need to control vectors, how quickly we can develop a vaccine, and how long the epidemic will continue. While these are important discussions to have, they are irrelevant if the world does not recognize and address a crucial reason why these explosive epidemics continue to occur in the first place: the world must talk about urban slums.Zika is, and will continue to be, a disease of the urban poor. Slum-defining characteristics-poor water and sanitation infrastructure, crowding, and poor structural quality of housing-offer ample opportunities for mosquitoes to breed and spread the Zika virus. It was recently estimated that 1.6 million childbearing women and 93 million people will be infected in the Americas’ first epidemic wave [2]. From this reservoir of infections, the world is witnessing the largest epidemic ever of a congenital complication-microcephaly. Except for sporadic reports, largely absent from discussion is the fact that the greatest proportion of Zika infections and its complications have occurred, and will continue to occur, among residents of the large, densely packed informal human settlements of Latin America and the Caribbean.

Syphilis and congenital syphilis (CS) are increasing in California (CA). From 2015 through 2019, for example, CA cases of early syphilis among reproductive-age females (15–44) and CS each increased by >200%. Certain populations—including people experiencing homelessness, using drugs, and/or belonging to certain racial/ethnic groups—have been disproportionately impacted. We hypothesized that geospatial social determinants of health (SDH) contribute to such health inequities. To demonstrate this, we geospatially described syphilis in CA using the Healthy Places Index (HPI). The HPI is a composite index that assigns a score to each CA census tract based on eight socioeconomic characteristics associated with health (education, housing, transportation, neighborhood conditions, clean environment, and healthcare access as well as economic and social resources). We divided CA census tracts into four quartiles based on HPI scores (with the lowest quartile having the least healthy socioeconomic and environmental conditions), then used 2013–2020 CA sexually transmitted diseases surveillance data to compare overall syphilis (among adults and adolescents) and CS case counts, incidence rates (per 100,000 population or live births), and incidence rate ratios (IRRs) among these quartiles. From 2013 to 2020, across all stages of syphilis and CS, disease burden was greatest in the lowest HPI quartile and smallest in the highest quartile (8308 cases (representing 33.2% of all incidents) versus 3768 (15.1%) for primary and secondary (P&S) syphilis; 5724 (31.6%) versus 2936 (16.2%) for early non-primary non-secondary (NPNS) syphilis; 11,736 (41.9%) versus 3026 (10.8%) for late/unknown duration syphilis; and 849 (61.9%) versus 57 (4.2%) for CS; all with p < 0.001). Using the highest HPI quartile as a reference, the IRRs in the lowest quartile were 17 for CS, 4.5 for late/unknown duration syphilis, 2.6 for P&S syphilis, and 2.3 for early NPNS syphilis. We thus observed a direct relationship between less healthy conditions (per HPI) and syphilis/CS in California, supporting our hypothesis that SDH correlate with disparities in syphilis, especially CS. HPI could inform allocation of resources to: (1) support communities most in need of assistance in preventing syphilis/CS cases and (2) reduce health disparities.

Background Colonization with Staphylococcus aureus is a well-defined risk factor for disease in hospitals, which can range from minor skin infections to severe, systemic diseases. However, the generalizability of this finding has not been thoroughly investigated outside of the hospital environment. We aimed to assess the role of S. aureus colonization as a risk factor for disease in the community. Methods We performed a meta-analysis of observational studies and searched PubMed for articles published between December 1979 and May 23, 2016. We included cohort, cross-sectional, and case-control studies that reported quantitative estimates of both S. aureus colonization and disease statuses of all study subjects. We excluded studies on recently hospitalized subjects, long-term care facilities, surgery patients, dialysis patients, hospital staff, S. aureus outbreaks, and livestock-associated infections. Our meta-analysis was performed using random-effects analysis to obtain pooled odds ratios (ORs) to compare the odds of S. aureus disease with respect to S. aureus colonization status. Results We identified 3477 citations, of which 12 articles on 6998 subjects met the eligibility criteria. Overall, subjects colonized with S. aureus were more likely to progress to disease than those who were non-colonized: (OR 1.87, 95% CI 1.21–2.88, n  = 7 studies). We observed a larger effect with methicillin-resistant S. aureus colonization (7.06, 4.60–10.84, n  = 7 studies). However, the methicillin-sensitive S. aureus colonization was not associated with greater odds of disease (1.20, 0.69–2.06, n  = 4 studies). Heterogeneity was present across studies in all of the subgroups: S. aureus (I 2  = 95.0%, χ 2 = 120.3, p  < 0.001), MRSA (I 2  = 92.8%, χ 2 = 82.8, p  =  p  < 0.001), and MSSA (I 2  = 86.3%, χ 2 = 21.8, p  < 0.001). Conclusions While the majority of papers individually support the assumption that colonization is a risk factor for S. aureus disease in the general population, there is marked heterogeneity between studies and further investigation is needed to identify the major sources of this variance. There is a shortage of literature addressing this topic in the community setting and a need for further research on colonization as a focus for disease prevention.

Objectives. To characterize the intersection of social determinants of health, measured as the availability of community opportunities for healthy living, and sexually transmitted infections (STIs) in California. Methods. Geocoded 2013–2021 California bacterial STI cases were aggregated into Healthy Places Index (HPI) quartiles. Communities in the lowest scoring HPI quartile have the fewest opportunities for healthy living, while communities in the highest scoring quartile have the most opportunities. Results. As community opportunities became more available, bacterial STI risk decreased. Asian people had the lowest bacterial STI rates, while Black/African American people had the highest. As community opportunities increased, White people had the largest overall STI risk reduction, Native Hawaiian and other Pacific Islander people had the smallest reduction, Hispanic/Latino people had equivalent gonorrhea and early syphilis risk, and American Indian/Alaska Native people had equivalent chlamydia risk. Conclusions. Although STI incidence decreased as community opportunities increased, people of different racial and ethnic identities were differentially affected. Because the availability of community opportunities is not enough to mitigate racial health disparities, more work is needed to ensure community-level STI prevention efforts are accessible and inclusive. ( Am J Public Health. 2025;115(5):799–807. https://doi.org/10.2105/AJPH.2024.307963 )