Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination - Kentucky, May-June 2021.

Although laboratory evidence suggests that antibody responses following COVID-19 vaccination provide better neutralization of some circulating variants than does natural infection (1,2), few real-world epidemiologic studies exist to support the benefit of vaccination for previously infected persons. This report details the findings of a case-control evaluation of the association between vaccination and SARS-CoV-2 reinfection in Kentucky during May-June 2021 among persons previously infected with SARS-CoV-2 in 2020. Kentucky residents who were not vaccinated had 2.34 times the odds of reinfection compared with those who were fully vaccinated (odds ratio [OR] = 2.34; 95% confidence interval [CI] = 1.58-3.47). These findings suggest that among persons with previous SARS-CoV-2 infection, full vaccination provides additional protection against reinfection. To reduce their risk of infection, all eligible persons should be offered vaccination, even if they have been previously infected with SARS-CoV-2.

Increased Risk of Late-onset Streptococcus pneumoniae Meningitis in Adults With Prior Head or Spine Surgeries.

In a case-control study within the Kaiser Permanente Northern California adult population, prior head or spine surgery was associated with increased Streptococcus pneumoniae meningitis outside of the postoperative period (no prior head or spine surgery; odds ratio, 6.0 [95% confidence interval, 1.9-18.6]). Among the cases, only 33.3% had received any prior pneumococcal vaccinations.

Barriers to Receipt of Prenatal Tetanus Toxoid, Reduced Diphtheria Toxoid, and Acellular Pertussis Vaccine Among Mothers of Infants Aged <4 Months with Pertussis - California, 2016.

Vaccination with tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine is recommended for all pregnant women to protect infants who are too young for vaccination from severe pertussis-related outcomes (1-3). However, Tdap vaccine coverage among pregnant women remains suboptimal in California (4). California mothers whose infants developed pertussis in 2016 and their prenatal care providers were interviewed to ascertain possible reasons for low Tdap vaccine coverage. Mothers who were offered Tdap vaccination on-site during a routine prenatal visit were more likely to be vaccinated than were mothers who were referred off-site for vaccination. Mothers insured by Medicaid were less likely to receive Tdap vaccine than were mothers with private insurance, even when the vaccine was stocked on-site. Nearly all vaccinated mothers received Tdap vaccine in their prenatal clinic. Incorporating Tdap vaccination into routine prenatal care visits is an effective means to increase prenatal Tdap vaccination coverage.

Effectiveness of Prenatal Tetanus, Diphtheria, and Acellular Pertussis Vaccination on Pertussis Severity in Infants.

BACKGROUND: All US women are recommended to receive a tetanus, diphtheria, and acellular pertussis (Tdap) vaccine at 27-36 weeks gestation during each pregnancy to reduce the risk of pertussis to their infants. The impact of this strategy on severity of disease among infected infants has not been evaluated. METHODS: We use a retrospective cohort study design evaluating whether pertussis-infected infants born in 2011-2015 whose mothers received Tdap vaccine during pregnancy had less severe pertussis, resulting in a lower risk of hospitalization or intensive care unit admission compared with infants born to unvaccinated mothers. RESULTS: Infected infants of vaccinated mothers were significantly less likely to be hospitalized and had significantly shorter hospital stays compared with infants born to unvaccinated mothers, after adjustment for chronological and gestational age and receipt of diphtheria and tetanus toxoids and acellular pertussis vaccine. Unadjusted and adjusted vaccine effectiveness for preventing hospitalization among infants with pertussis was 72% (95% confidence interval [CI], 49%-85%) and 58% (95% CI 15%-80%), respectively. No infants born to vaccinated mothers required intubation or died of pertussis. CONCLUSIONS: Infants with pertussis whose mothers received Tdap during pregnancy had a significantly lower risk of hospitalization and intensive care unit admission and shorter hospital stays. Prenatal Tdap vaccination is a critical strategy for reducing the morbidity and mortality from pertussis.

A Population-Based Study of Recurrent Symptomatic Bordetella pertussis Infections in Children in California, 2010-2015.

BACKGROUND: Natural infection with Bordetella pertussis is thought to result in 4-20 years of immunity against subsequent symptomatic pertussis infection. However, these estimates are based on studies in unvaccinated or whole-cell pertussis-vaccinated children. We conducted a population-based study of pertussis infection and reinfection during a 5-year period in California in an cohort vaccinated exclusively with acellular pertussis (aP) vaccine. METHODS: California surveillance data were reviewed to identify all children with 2 reported incidents of pertussis with symptom onset between 1 January 2010 and 31 December 2015. Case investigation reports were reviewed, and children with ≥2 episodes of symptomatic pertussis infection that met the case definition were included. RESULTS: Of 26259 pertussis cases reported in children (aged <18 years), 27 children met the inclusion criteria. Recurrent cases occurred among children of all ages; 5 (19%) were <6 months of age at the time of their first illness. The time from initial infection to reinfection was <1 year in 11 (41%) cases. Twenty-one children (78%) had received ≥3 doses of diphtheria and tetanus toxoids and aP vaccine at the time of their first pertussis infection, 1 (4%) had received 1 dose, and 5 (19%) were unvaccinated. CONCLUSIONS: Recurrent cases of pertussis infection are extremely rare. Based on this surveillance data, approximately 0.1% of children who were infected with pertussis experienced a clinically significant second episode of pertussis within 4 years. More research is needed to understand the immune response to B. pertussis infection in children vaccinated with aP vaccines.

Serum Bactericidal Antibody Responses of Students Immunized With a Meningococcal Serogroup B Vaccine in Response to an Outbreak on a University Campus.

Background: MenB-4C is a recently licensed meningococcal serogroup B vaccine. For vaccine licensure, short-term efficacy was inferred from serum bactericidal antibody (SBA) titers against 3 antigen-specific indicator strains, which are not necessarily representative of US disease-causing strains. Methods: A total of 4923 students were immunized with MenB-4C in response to an outbreak at a university. Serum samples were obtained at 1.5-2 months from 106 students who received the recommended 2 doses and 52 unvaccinated students. Follow-up serum samples were obtained at 7 months from 42 vaccinated and 24 unvaccinated participants. SBA was measured against strains from 4 university outbreaks. Results: At 1.5-2 months, the proportion of immunized students with protective titers ≥1:4 against an isolate from the campus outbreak was 93% (95% confidence interval [CI], 87%-97%) vs 37% (95% CI, 24%-51%) in unvaccinated students. The proportion with protective titers against strains from 3 other university outbreaks was 73% (95% CI, 62%-82%) vs 26% (95% CI, 14%-41%) in unvaccinated; 71% (95% CI, 61%-79%) vs 19% (95% CI, 10%-33%) in unvaccinated; and 53% (95% CI, 42%-64%) vs 9% (95% CI, 3%-22%) in unvaccinated (P < .0001 for each strain). At 7 months, the proportion of immunized students with titers ≥1:4 was 86% (95% CI, 71%-95%) against the isolate from the campus outbreak and 57% (95% CI, 41%-72%), 38% (95% CI, 24%-54%), and 31% (95% CI, 18%-47%), respectively, for the other 3 outbreak strains. Conclusions: MenB-4C elicited short-term protective titers against 4 strains responsible for recent university campus outbreaks. By 7 months the prevalence of protective titers was <40% for 2 of the 4 outbreak strains. A booster dose of MenB-4C may be needed to maintain protective titers.

Effectiveness of Prenatal Versus Postpartum Tetanus, Diphtheria, and Acellular Pertussis Vaccination in Preventing Infant Pertussis.

BACKGROUND: Most severe and fatal cases of pertussis occur in infants <8 weeks of age, before initiation of the primary pertussis vaccine series. Women are recommended to receive tetanus, diphtheria, and acellular pertussis (Tdap) vaccine at the start of the third trimester of each pregnancy to optimize transplacental transfer of antibodies to the fetus. This recommendation was made by the Advisory Committee for Immunization Practices based on immunogenicity data, and no studies in the United States have yet evaluated the effectiveness of this strategy in reducing pertussis incidence in infants. METHODS: We evaluated a cohort of mothers with documented Tdap vaccination histories in the California Immunization Registry to determine whether infants whose mothers received Tdap vaccine at 27-36 weeks gestation had a lower risk of pertussis at <8 weeks of age than infants born to women who received Tdap vaccine within 14 days post partum. RESULTS: Tdap vaccination received at 27-36 weeks gestation was found to be 85% (95% confidence interval, 33%-98%) more effective than postpartum Tdap vaccination at preventing pertussis in infants <8 weeks of age . Vaccination at 27-36 weeks gestation was more effective at preventing pertussis in infant than vaccination during the second trimester. CONCLUSIONS: Tdap vaccination at 27-36 weeks gestation was 85% more effective than postpartum vaccination at preventing pertussis in infants <8 weeks of age. Efforts should be made by prenatal care providers to provide Tdap vaccine to pregnant women during routine prenatal visits at the earliest opportunity between 27 and 36 weeks gestation.

Subacute Sclerosing Panencephalitis: The Devastating Measles Complication That Might Be More Common Than Previously Estimated.

BACKGROUND: Subacute sclerosing panencephalitis (SSPE) is a fatal complication of measles. We reviewed California cases from 1998-2015 to understand risk factors for SPPE and estimate incidence. METHODS: SSPE cases had clinically compatible symptoms and measles antibody detection in cerebrospinal fluid (CSF) or medical record documentation of SSPE. Cases were identified though a state death certificate search, Centers for Disease Control and Prevention reports, or investigations for undiagnosed neurologic disease. Measles detection in CSF was performed by serology at the California Department of Public Health or at clinical laboratories. RESULTS: Seventeen SSPE cases were identified. Males outnumbered females 2.4:1. Twelve (71%) cases had a history of measles-like illness; all 12 had illness prior to 15 months of age. Eight (67%) children were exposed to measles in California. SSPE was diagnosed at a median age of 12 years (3-35 years), with a latency period of 9.5 years (2.5-34 years). Among measles cases reported to CDPH during 1988-1991, the incidence of SSPE was 1:1367 for children <5 years, and 1:609 for children <12 months at time of measles disease. CONCLUSIONS: SSPE cases in California occurred at a high rate among unvaccinated children, particularly those infected during infancy. Protection of unvaccinated infants requires avoidance of travel to endemic areas, or early vaccination prior to travel at age 6-11 months. Clinicians should be aware of SSPE in patients with compatible symptoms, even in older patients with no specific history of measles infection. SSPE demonstrates the high human cost of "natural" measles immunity.

Increased Risk for Meningococcal Disease Among Men Who Have Sex With Men in the United States, 2012-2015.

BACKGROUND: Several clusters of serogroup C meningococcal disease among men who have sex with men (MSM) have been reported in the United States in recent years. The epidemiology and risk of meningococcal disease among MSM is not well described. METHODS: All meningococcal disease cases among men aged 18-64 years reported to the National Notifiable Disease Surveillance System between January 2012 and June 2015 were reviewed. Characteristics of meningococcal disease cases among MSM and men not known to be MSM (non-MSM) were described. Annualized incidence rates among MSM and non-MSM were compared through calculation of the relative risk and 95% confidence intervals. Isolates from meningococcal disease cases among MSM were characterized using standard microbiological methods and whole-genome sequencing. RESULTS: Seventy-four cases of meningococcal disease were reported among MSM and 453 among non-MSM. Annualized incidence of meningococcal disease among MSM was 0.56 cases per 100000 population, compared to 0.14 among non-MSM, for a relative risk of 4.0 (95% confidence interval [CI], 3.1-5.1). Among the 64 MSM with known status, 38 (59%) were infected with human immunodeficiency virus (HIV). HIV-infected MSM had 10.1 times (95% CI, 6.1-16.6) the risk of HIV-uninfected MSM. All isolates from cluster-associated cases were serogroup C sequence type 11. CONCLUSIONS: MSM are at increased risk for meningococcal disease, although the incidence of disease remains low. HIV infection may be an important factor for this increased risk. Routine vaccination of HIV-infected persons with a quadrivalent meningococcal conjugate vaccine in accordance with Advisory Committee on Immunization Practices recommendations should be encouraged.

Notes from the Field: Outbreak of Serogroup B Meningococcal Disease at a University - California, 2016.

On January 31, 2016, the Santa Clara County Public Health Department (SCCPHD) was notified of a suspected case of meningococcal disease in a university undergraduate student. By February 2, two additional suspected cases had been reported in undergraduate students living on the same campus. The index patient (patient A) required intensive care, whereas patients B and C had milder illness; there were no deaths. All three patients were part of overlapping social networks and had attended the same events during the week before the onset of patient A's symptoms, but whether they had direct contact with one another could not be verified. Serogroup B Neisseria meningitidis was identified in cerebrospinal fluid and blood from patient A and in blood from patient B. Serogroup B has been responsible for all U.S. college outbreaks of meningococcal disease since 2011 (1). Laboratory results for patient C were inconclusive.

Outbreak of Serogroup C Meningococcal Disease Primarily Affecting Men Who Have Sex with Men - Southern California, 2016.

During March 4-August 11, 2016, 25 outbreak-associated cases of meningococcal disease, including two deaths (8% case-fatality ratio), were reported in Southern California. Twenty-four of the cases were caused by serogroup C Neisseria meningitidis (NmC) and one by N. meningitidis with an undetermined serogroup (Figure). On June 24, 2016, in response to this increase in NmC cases, primarily among men who have sex with men (MSM) in Los Angeles County, the city of Long Beach, and Orange County, the California Department of Public Health (CDPH) issued a press release and health advisory, declaring an outbreak of NmC in Southern California (1).

Risk Factors Associated With Infant Deaths From Pertussis: A Case-Control Study.

BACKGROUND: In the current era, most pertussis deaths occur in infants <3 months of age. Leukocytosis with lymphocytosis and pneumonia are commonly observed among cases of severe pertussis. METHODS: Risk factors associated with fatal pertussis were identified by comparing fatal pertussis cases among patients <120 days of age occurring from 1 January 1998 through 26 December 2014, matched by age (<120 days), county of residence, and closest symptom onset date with 1-4 nonfatal hospitalized cases. California Department of Public Health surveillance data were reviewed to identify cases; demographics, clinical presentation, and course were abstracted from corresponding birth and medical records. Logistic regression and classification tree analyses were used to examine the risk of fatal pertussis with respect to identified factors. RESULTS: Fifty-three fatal infant pertussis cases were identified and compared with 183 nonfatal hospitalized pertussis cases. Fatal cases had significantly lower birth weight, younger gestational age, younger age at time of cough onset, and higher peak white blood cell (WBC) and lymphocyte counts. Fatal cases were less likely to have received macrolide antibiotics and more likely to have received steroids or nitric oxide and to develop pulmonary hypertension, seizures, encephalitis, and pneumonia. Additionally, exchange transfusion, extracorporeal membrane oxygenation, and intubation occurred significantly more frequently among fatal cases. In multivariate analyses, peak WBC count, birth weight, intubation, and receipt of nitric oxide were predictors of death. CONCLUSIONS: Early recognition of pertussis in young infants and treatment with appropriate antibiotic therapy are important in preventing death. Several risk factors are strongly associated with fatal pertussis in infants.

Missed opportunities for tetanus postexposure prophylaxis--California, January 2008-March 2014.

Tetanus is an acute and sometimes fatal disease characterized by sudden muscle contractions. The number of tetanus cases reported annually in the United States has declined significantly since the 1930s and 1940s as a result of the introduction of tetanus vaccines. However, sporadic cases continue to occur in persons who are not up-to-date with tetanus toxoid-containing vaccinations (TT) and do not receive appropriate postexposure prophylaxis (PEP). To assess the extent of these cases, the California Department of Public Health reviewed all tetanus cases reported during January 2008-March 2014. A total of 21 tetanus patients were reported; five (24%) died. An average of three cases were reported each year during 2008-2013; the average annual incidence among patients aged ≥65 years (0.23 cases per 1 million population) was twice that among patients aged 21-64 years (0.10 cases per 1 million population). Of 16 patients with an acute injury before illness and diagnosis, nine (56%) sought medical care, and two (22%) of the nine received appropriate PEP. Although tetanus is rare, it is a life-threatening disease that is preventable. Health care providers should ensure that their patients are up-to-date with TT vaccination and provide appropriate postexposure prophylaxis for patients with wounds.

Measles outbreak--California, December 2014-February 2015.

On January 5, 2015, the California Department of Public Health (CDPH) was notified about a suspected measles case. The patient was a hospitalized, unvaccinated child, aged 11 years with rash onset on December 28. The only notable travel history during the exposure period was a visit to one of two adjacent Disney theme parks located in Orange County, California. On the same day, CDPH received reports of four additional suspected measles cases in California residents and two in Utah residents, all of whom reported visiting one or both Disney theme parks during December 17-20. By January 7,seven California measles cases had been confirmed, and CDPH issued a press release and an Epidemic Information Exchange (Epi-X) notification to other states regarding this outbreak. Measles transmission is ongoing.

Meningococcal disease among men who have sex with men - United States, January 2012-June 2015.

Since 2012, three clusters of serogroup C meningococcal disease among men who have sex with men (MSM) have been reported in the United States. During 2012, 13 cases of meningococcal disease among MSM were reported by the New York City Department of Health and Mental Hygiene (1); over a 5-month period during 2012­2013, the Los Angeles County Department of Public Health reported four cases among MSM; and during May­June 2015, the Chicago Department of Public Health reported seven cases of meningococcal disease among MSM in the greater Chicago area. MSM have not previously been considered at increased risk for meningococcal disease. Determining outbreak thresholds* for special populations of unknown size (such as MSM) can be difficult. The New York City health department declared an outbreak based on an estimated increased risk for meningococcal infection in 2012 among MSM and human immunodeficiency virus (HIV)­infected MSM compared with city residents who were not MSM or for whom MSM status was unknown (1). The Chicago Department of Public Health also declared an outbreak based on an increase in case counts and thresholds calculated using population estimates of MSM and HIV-infected MSM. Local public health response included increasing awareness among MSM, conducting contact tracing and providing chemoprophylaxis to close contacts, and offering vaccination to the population at risk (1­3). To better understand the epidemiology and burden of meningococcal disease in MSM populations in the United States and to inform recommendations, CDC analyzed data from a retrospective review of reported cases from January 2012 through June 2015.

Pertussis epidemic--California, 2014.

On June 13, 2014, the California Department of Public Health (CDPH) declared that a pertussis epidemic was occurring in the state when reported incidence was more than five times greater than baseline levels. The incidence of pertussis in the United States is cyclical, with peaks every 3-5 years, as the number of susceptible persons in the population increases. The last pertussis epidemic in California occurred in 2010, when approximately 9,000 cases were reported, including 808 hospitalizations and 10 infant deaths, for a statewide incidence of 24.6 cases per 100,000 population. During January 1-November 26, 2014, a total of 9,935 cases of pertussis with onset in 2014 were reported to CDPH, for a statewide incidence of 26.0 cases per 100,000. CDPH is working closely with local health departments to prioritize public health activities, with the primary goal of preventing severe cases of pertussis, which typically occurs in infants. All prenatal care providers are being encouraged to provide tetanus, diphtheria, and acellular pertussis vaccine (Tdap) to pregnant women during each pregnancy, ideally at 27-36 weeks' gestation, as is recommended by the Advisory Committee on Immunization Practices (ACIP), or refer patients to an alternative provider, such as a pharmacy or local public health department, to receive Tdap.

Risk factors of carbapenemase-producing Enterobacterales acquisition among adult intensive care unit patients at a Kentucky Academic Medical Center.

Background: Acquisition of carbapenemase-producing carbapenem-resistant Enterobacterales (CP-CRE) are associated with negative health outcomes. Our adult intensive care unit (ICU) population has experienced low levels of CP-CRE acquisition; however, specific risk factors for this population at our medical facility have not been studied. Aims: To identify risk factors of CP-CRE acquisition and describe CP-CRE epidemiology among adult ICU patients at our medical facility. Methods: A retrospective cohort study was performed at a Kentucky Academic Medical Center. Surveillance specimens were collected at admission and weekly thereafter to identify CP-CRE colonization. Clinical data were extracted from patient medical records. Cases were defined as those who tested positive for CP-CRE on ICU admission day 3 or greater. Risk of CP-CRE acquisition was calculated using Modified Poisson regression. Findings: Independent risk factors of CP-CRE acquisition included administration of enteral tube feeds (risk ratio [RR], 4.46; 95% confidence interval [CI], 1.74-11.43); diagnosis of Clostridioides difficile enterocolitis (RR, 3.51; 95% CI, 1.27-9.68), pressure ulcer (RR, 3.48; 95% CI, 1.91-6.36), and morbid obesity (RR, 2.10; 95% CI, 1.12-3.95); having a drainage tube (RR, 2.63; 95% CI, 1.38-4.98); admission to a medical ICU (RR, 2.39; 95% CI, 1.32-4.35); 90-day use of a carbapenem (RR, 2.27; 95% CI, 1.21-4.26); and dialysis procedure (RR, 2.22; 95% CI, 1.15-4.27). Conclusion: Most CP-CRE risk factors were associated with alteration of colon microbiota and/or invasive procedures/devices. These results will assist in creating a more targeted CP-CRE active surveillance system and highlight areas for infection prevention intervention.

Characteristics of Decedents With COVID-19-Related Mortality in Kentucky, July 1-August 13, 2021.

OBJECTIVE: Although vaccination reduces the risk of severe COVID-19, fatal COVID-19 cases after vaccination can occur. We examined the characteristics of decedents with COVID-19-related mortality to help inform discussions about vaccination, boosters, and mitigation strategies. METHODS: We examined COVID-19-related deaths in Kentucky resulting from infections occurring from July 1 through August 13, 2021. We used records from case investigations, medical records, the Kentucky Health Information Exchange, and the Kentucky Immunization Registry to determine demographic information, vaccination status, and underlying health conditions, including calculation of the Charlson Comorbidity Index (CCI). We calculated mortality incidence rates by vaccination status by using data for unvaccinated and fully vaccinated populations in Kentucky as of July 1, 2021. RESULTS: In total, 777 COVID-19-related deaths occurred in Kentucky during the study period; 592 (76.2%) occurred among unvaccinated people. Compared with unvaccinated decedents, fully vaccinated decedents were older (median age, 77 vs 65 years; P < .001), had higher comorbidity levels (median CCI, 3 vs 1; P < .001), and were more likely to have immunocompromised health status (26.4% vs 16.0%; P = .003). Diabetes, hypertension, heart disease, and chronic lung disease were more common among vaccinated decedents than among unvaccinated decedents. Unvaccinated adults had a significantly higher risk of death than fully vaccinated adults (incidence rate ratio for age 20-49 years: 20.5 [95% CI, 6.5-64.8]; 50-64 years: 14.6 [95% CI, 9.4-22.7]; ≥65 years: 10.2 [95% CI, 8.3-12.4]). CONCLUSIONS: Immunocompromised health status, older age, and higher comorbidity were prevalent among fully vaccinated decedents, suggesting adults with these characteristics may benefit from additional protection strategies. Further understanding of the protection of additional and booster doses is needed.

A population-based study of neurologic manifestations of severe influenza A(H1N1)pdm09 in California.

BACKGROUND: Reported influenza-associated neurologic complications are generally limited to case series or case reports. We conducted a population-based study of neurologic manifestations associated with severe and fatal influenza A(H1N1)pdm09 (2009 H1N1) cases. METHODS: Medical records of patients with fatal or severe (hospitalized in intensive care unit) laboratory-confirmed 2009 H1N1 reported to the California Department of Public Health from 15 April 2009 through 31 December 2009 were reviewed to identify those with primary neurological manifestations. Cases with secondary neurologic manifestations (eg, hypoxia) were excluded. Primary influenza-associated neurologic complications (INCs) were classified into 4 groups: encephalopathy/encephalitis, seizures, meningitis, and other. Severe 2009 H1N1-associated neurologic incidence was calculated by using estimates of 2009 H1N1 illnesses in California. RESULTS: Of 2069 reported severe or fatal 2009 H1N1 cases, 419 (20%) had neurologic manifestations. Of these, 77 (18%) met our definition of INCs: encephalopathy/encephalitis (n = 29), seizures (n = 44), meningitis (n = 3), and other (Guillain-Barré Syndrome) (n = 1). The median age was 9 years (range, 4 months-92 years); the highest rate of disease was among pediatric Asian/Pacific Islanders (12.79 per 1,000,000) compared with pediatric white, non-Hispanics (3.09 per 1,000,000), Hispanics (4.58 per 1,000,000), and blacks (6.57 per 1,000,000). The median length of stay (LOS) was 4 days (range, 1-142), and there were 4 fatalities. The estimated incidence of INCs was 1.2 per 100,000 symptomatic 2009 H1N1 illnesses. CONCLUSIONS: Influenza-associated neurologic complications were observed in 4% of patients with fatal or severe 2009 H1N1. They were observed most often in pediatric patients, and Asian/Pacific Islanders appear to be overrepresented compared with the California population. Most patients with INCs had a relatively short LOS, and there were few fatalities.