Early warning system for West Nile virus risk areas, California, USA.

The Dynamic Continuous-Area Space-Time (DYCAST) system is a biologically based spatiotemporal model that uses public reports of dead birds to identify areas at high risk for West Nile virus (WNV) transmission to humans. In 2005, during a statewide epidemic of WNV (880 cases), the California Department of Public Health prospectively implemented DYCAST over 32,517 km2 in California. Daily risk maps were made available online and used by local agencies to target public education campaigns, surveillance, and mosquito control. DYCAST had 80.8% sensitivity and 90.6% specificity for predicting human cases, and k analysis indicated moderate strength of chance-adjusted agreement for >4 weeks. High-risk grid cells (populations) were identified an average of 37.2 days before onset of human illness; relative risk for disease was >39× higher than for low-risk cells. Although prediction rates declined in subsequent years, results indicate DYCAST was a timely and effective early warning system during the severe 2005 epidemic.

A review of adult mortality due to 2009 pandemic (H1N1) influenza A in California.

BACKGROUND: While children and young adults had the highest attack rates due to 2009 pandemic (H1N1) influenza A (2009 H1N1), studies of hospitalized cases noted high fatality in older adults. We analyzed California public health surveillance data to better characterize the populations at risk for dying due to 2009 H1N1. METHODS AND FINDINGS: A case was an adult ≥20 years who died with influenza-like symptoms and laboratory results indicative of 2009 H1N1. Demographic and clinical data were abstracted from medical records using a standardized case report form. From April 3, 2009-August 10, 2010, 541 fatal cases ≥20 years with 2009 H1N1 were reported. Influenza fatality rates per 100,000 population were highest in persons 50-59 years (3.5; annualized rate = 2.6) and 60-69 years (2.3; annualized rate = 1.7) compared to younger and older age groups (0.4-1.9; annualized rates = 0.3-1.4). Of 486 cases hospitalized prior to death, 441 (91%) required intensive care unit (ICU) admission. ICU admission rates per 100,000 population were highest in adults 50-59 years (8.6). ICU case-fatality ratios among adults ranged from 24-42%, with the highest ratios in persons 70-79 years. A total of 425 (80%) cases had co-morbid conditions associated with severe seasonal influenza. The prevalence of most co-morbid conditions increased with increasing age, but obesity, pregnancy and obstructive sleep apnea decreased with age. Rapid testing was positive in 97 (35%) of 276 tested. Of 482 cases with available data, 384 (80%) received antiviral treatment, including 49 (15%) of 328 within 48 hours of symptom onset. CONCLUSIONS: Adults aged 50-59 years had the highest fatality due to 2009 H1N1; older adults may have been spared due to pre-existing immunity. However, once infected and hospitalized in intensive care, case-fatality ratios were high for all adults, especially in those over 60 years. Vaccination of adults older than 50 years should be encouraged.

Children hospitalized with 2009 novel influenza A(H1N1) in California.

OBJECTIVE: To describe clinical and epidemiologic features of 2009 novel influenza A(H1N1) in children. DESIGN: Analysis of data obtained from standardized report forms and medical records. SETTING: Statewide public health surveillance in California. PARTICIPANTS: Three hundred forty-five children who were hospitalized with or died of 2009 novel influenza A(H1N1). MAIN EXPOSURE: Laboratory-confirmed 2009 novel influenza A(H1N1). MAIN OUTCOME MEASURES: Hospitalization and death. RESULTS: From April 23 to August 11, 2009, 345 cases in children younger than 18 years were reported. The median age was 6 years. The hospitalization rate per 100 000 per 110 days was 3.5 (0.97 per 100 000 person-months), with rates highest in infants younger than 6 months (13.9 per 100 000 or 3.86 per 100 000 person-months). Two-thirds (230; 67%) had comorbidities. More than half (163 of 278; 59%) had pneumonia, 94 (27%) required intensive care, and 9 (3%) died; in 3 fatal cases (33%), children had secondary bacterial infections. More than two-thirds (221 of 319; 69%) received antiviral treatment, 44% (88 of 202) within 48 hours of symptom onset. In multivariate analysis, congenital heart disease (odds ratio [OR], 5.0; 95% confidence interval [CI], 1.9-13.5) and cerebral palsy/developmental delay (OR, 3.5; 95% CI, 1.7-7.4) were associated with increased likelihood of intensive care unit admission and/or death; likelihood was decreased in Hispanic (OR, 0.4; 95% CI, 0.2-0.8) and black (OR, 0.3; 95% CI, 0.1-1.0) children compared with white children. CONCLUSIONS: More than one-quarter of children hospitalized with 2009 novel influenza A(H1N1) reported to the California Department of Public Health required intensive care and/or died. Regardless of rapid test results, when 2009 novel influenza A(H1N1) is circulating, clinicians should maintain a high suspicion in children with febrile respiratory illness and promptly treat those with underlying risk factors, especially infants.

Invasive group A streptococcal infection concurrent with 2009 H1N1 influenza.

We describe 10 patients with 2009 H1N1 influenza and concurrent invasive group A streptococcal infection with marked associated morbidity and mortality. Seven patients required intensive care, 8 required mechanical ventilation, and 7 died. Five of the patients, including 4 of the fatalities, were previously healthy.

Factors associated with death or hospitalization due to pandemic 2009 influenza A(H1N1) infection in California.

CONTEXT: Pandemic influenza A(H1N1) emerged rapidly in California in April 2009. Preliminary comparisons with seasonal influenza suggest that pandemic 2009 influenza A(H1N1) disproportionately affects younger ages and causes generally mild disease. OBJECTIVE: To describe the clinical and epidemiologic features of pandemic 2009 influenza A(H1N1) cases that led to hospitalization or death. DESIGN, SETTING, AND PARTICIPANTS: Statewide enhanced public health surveillance of California residents who were hospitalized or died with laboratory evidence of pandemic 2009 influenza A(H1N1) infection reported to the California Department of Public Health between April 23 and August 11, 2009. MAIN OUTCOME MEASURE: Characteristics of hospitalized and fatal cases. RESULTS: During the study period there were 1088 cases of hospitalization or death due to pandemic 2009 influenza A(H1N1) infection reported in California. The median age was 27 years (range, <1-92 years) and 68% (741/1088) had risk factors for seasonal influenza complications. Sixty-six percent (547/833) of those with chest radiographs performed had infiltrates and 31% (340/1088) required intensive care. Rapid antigen tests were falsely negative in 34% (208/618) of cases evaluated. Secondary bacterial infection was identified in 4% (46/1088). Twenty-one percent (183/884) received no antiviral treatment. Overall fatality was 11% (118/1088) and was highest (18%-20%) in persons aged 50 years or older. The most common causes of death were viral pneumonia and acute respiratory distress syndrome. CONCLUSIONS: In the first 16 weeks of the current pandemic, the median age of hospitalized infected cases was younger than is common with seasonal influenza. Infants had the highest hospitalization rates and persons aged 50 years or older had the highest mortality rates once hospitalized. Most cases had established risk factors for complications of seasonal influenza.

Efficacy of aerial spraying of mosquito adulticide in reducing incidence of West Nile Virus, California, 2005.

Epidemic transmission of West Nile virus (WNV) in Sacramento County, California, in 2005 prompted aerial application of pyrethrin, a mosquito adulticide, over a large urban area. Statistical analyses of geographic information system datasets indicated that adulticiding reduced the number of human WNV cases within 2 treated areas compared with the untreated area of the county. When we adjusted for maximum incubation period of the virus from infection to onset of symptoms, no new cases were reported in either of the treated areas after adulticiding; 18 new cases were reported in the untreated area of Sacramento County during this time. Results indicated that the odds of infection after spraying were approximately 6x higher in the untreated area than in treated areas, and that the treatments successfully disrupted the WNV transmission cycle. Our results provide direct evidence that aerial mosquito adulticiding is effective in reducing human illness and potential death from WNV infection.

Genetic deficiency of chemokine receptor CCR5 is a strong risk factor for symptomatic West Nile virus infection: a meta-analysis of 4 cohorts in the US epidemic.

West Nile virus (WNV) causes disease in approximately 20% of infected humans. We previously reported that homozygosity for CCR5Delta32, a nonfunctional variant of chemokine receptor CCR5, is markedly increased among symptomatic WNV-seropositive patients from Arizona and Colorado. To confirm this, we analyzed cohorts from California and Illinois. An increase in CCR5-deficient subjects was found in both (for California, odds ratio [OR], 4.2 [95% confidence interval {CI}, 1.5-11.9] [P= .004]; for Illinois, OR, 3.1 [95% CI, 0.9-11.2] [P= .06]). A meta-analysis of all 4 cohorts showed an OR of 4.2 (95% CI, 2.1-8.3 [P= .0001]). Thus, CCR5 deficiency is a strong and consistent risk factor for symptomatic WNV infection in the United States.

Risk factors for West Nile virus neuroinvasive disease, California, 2005.

In 2005, 880 West Nile virus cases were reported in California; 305 case-patients exhibited neuroinvasive disease, including meningitis, encephalitis, or acute flaccid paralysis. Risk factors independently associated with developing neuroinvasive disease rather than West Nile fever included older age, male sex, hypertension, and diabetes mellitus.

Role of corvids in epidemiology of west Nile virus in southern California.

The invasion of different southern California landscapes by West Nile virus (WNV) and its subsequent amplification to epidemic levels during 2004 enabled us to study the impact of differing corvid populations in three biomes: the hot Colorado desert with few corvids (Coachella Valley), the southern San Joaquin Valley (Kern County) with large western scrub-jay but small American crow populations, and the cool maritime coast (Los Angeles) with a large clustered American crow population. Similar surveillance programs in all three areas monitored infection rates in mosquitoes, seroconversion rates in sentinel chickens, seroprevalence in wild birds, numbers of dead birds reported by the public, and the occurrence of human cases. Infection rates in Culex tarsalis Coquillett and sentinel chicken seroconversion rates were statistically similar among all three areas, indicating that highly competent mosquito hosts were capable of maintaining enzootic WNV transmission among less competent and widely distributed avian hosts, most likely house sparrows and house finches. In contrast, infection rates in Culex pipiens quinquefasciatus Say were statistically higher in Kern and Los Angeles counties with elevated corvid populations than in Coachella Valley with few corvids. Spatial analyses of dead corvids showed significant clusters near known American crow roosts in Los Angeles that were congruent with clusters of human cases. In this area, the incidence of human and Cx. p. quinquefasciatus infection was significantly greater within corvid clusters than without, indicating their importance in virus amplification and as a risk factor for human infection. In contrast the uniform dispersion by territorial western scrub-jays resulted in a high, but evenly distributed, incidence of human disease in Kern County.

2004 California pediatric West Nile virus case series.

Relatively few pediatric West Nile virus cases have been recognized in the United States since the virus was first identified in 1999. We reviewed the clinical characteristics of 23 cases in pediatric patients that occurred in California in 2004 to better understand the infection in this population.