Evolutionary dynamics of West Nile virus in the United States, 1999-2011: phylogeny, selection pressure and evolutionary time-scale analysis

West Nile virus (WNV), an arbovirus maintained in a bird-mosquito enzootic cycle, can infect other vertebrates including humans. WNV was first reported in the US in 1999 where, to date, three genotypes belonging to WNV lineage I have been described (NY99, WN02, SW/WN03). We report here the WNV sequences obtained from two birds, one mosquito, and 29 selected human samples acquired during the US epidemics from 2006–2011 and our examination of the evolutionary dynamics in the open-reading frame of WNV isolates reported from 1999–2011. Maximum-likelihood and Bayesian methods were used to perform the phylogenetic analyses and selection pressure analyses were conducted with the HyPhy package. Phylogenetic analysis identified human WNV isolates within the main WNV genotypes that have circulated in the US. Within genotype SW/WN03, we have identified a cluster with strains derived from blood donors and birds from Idaho and North Dakota collected during 2006–2007, termed here MW/WN06. Using different codon-based and branch-site selection models, we detected a number of codons subjected to positive pressure in WNV genes. The mean nucleotide substitution rate for WNV isolates obtained from humans was calculated to be 5.06×10⁻⁴ substitutions/site/year (s/s/y). The Bayesian skyline plot shows that after a period of high genetic variability following the introduction of WNV into the US, the WNV population appears to have reached genetic stability. The establishment of WNV in the US represents a unique opportunity to understand how an arbovirus adapts and evolves in a naïve environment. We describe a novel, well-supported cluster of WNV formed by strains collected from humans and birds from Idaho and North Dakota. Adequate genetic surveillance is essential to public health since new mutants could potentially affect viral pathogenesis, decrease performance of diagnostic assays, and negatively impact the efficacy of vaccines and the development of specific therapies.

West Nile Virus (WNV) is a mosquito-borne virus of African origin that is widespread around the world. The WNV life-cycle involves mosquitoes and birds, but humans and other animals can be infected, although they are not considered to be important players in the transmission cycle. Clinically, most WNV infections are unapparent, but the virus can disseminate to the central nervous system causing a potentially fatal neurological disease, especially in susceptible populations including elderly and immunocompromised individuals. West Nile virus can also be transmitted by organ transplant and by transfusion of blood and blood components. Like other arboviruses, WNV has the extraordinary capacity of growing in the different microenvironments represented by the invertebrate vector and the vertebrate hosts. From an evolutionary standpoint, the arrival of WNV in the US in 1999 represents a unique opportunity to explore the processes involved in the adaptation and dissemination of an arbovirus in a naïve environment. From the study of WNV sequences, we can not only learn about the evolutionary mechanisms that govern arboviruses, but also update diagnostic tests that rely on the detection of the viral genome upon the occurrence of mutations and study the existence of genetic markers that may be responsible for increases in clinical cases and their severity.

Abstract 170: Racial differences in stage at diagnosis and survival for premenopausal breast cancer patients

BACKGROUND: There are racial/ ethnic disparities in breast cancer survival rates in the US. Tumor stage at diagnosis has long been a prognostic factor in breast cancer. Our objective was to determine whether there are racial disparities in tumor stage at diagnosis of breast cancer in pre-menopausal women, using a large national cancer registry.

METHODS: We conducted a retrospective analysis using data from the Surveillance Epidemiology and End Results database for 1996-2006. Premenopausal (≤50 years) women with primary diagnosis of breast cancer were identified using appropriate ICD-O-3 codes (C500-C509). Comparing racial/ethnic groups, with white race as the reference, multivariate logistic regression was used to assess the odds of late stage (stage III or IV) versus early stage (stage I or II) diagnosis at presentation, adjusting for prognostic factors, tumor characteristics, and year differences. All statistical tests were two-sided.

RESULTS: A total of 86,570 women met our inclusion criteria. Of those, 56,811 (65.62%) were White, 10,789 (12.46%) were Hispanic, 9,896 (11.43%) were Black, 8,115 (9.37%) were Asian or Pacific Islanders, 544 (0.63%) were Native American and for 415 (0.48%) women the race was unknown. A majority of patients were 46-50 years old (43%) and married (65%) at the time of diagnosis. Most were diagnosed with stage II (46%), invasive ductal (93%) histology, 1.1-2cm (36%) in size, poorly differentiated (45%), and without distant metastasis (96%). On multivariate analysis, compared to white women, Black women had 58% higher adjusted odds (OR: 1.58; 95% CI: 1.49-1.68) and Hispanic women had 37% higher odds (OR: 1.37; 95%CI: 1.29-1.46) of having late stage versus early stage breast cancer at time of diagnosis. Figure 1 shows the race specific percent of women diagnosed with late stage cancer across the years. Cancer-specific mortality rates were 10.1% for whites, 21.1% for blacks, 13.4% for Hispanics, 17.6% for Native Americans, and 9.6 % for Asians (p value <.001).

CONCLUSIONS: Utilizing a large cohort of premenopausal women diagnosed with breast cancer our study showed African-American and Hispanic women have higher incidence of diagnosis of late stage breast cancer as compared to their white counterparts. They as well as Native Americans also have higher cancer specific mortality rates as compared to their white and Asian counterparts. This study provides evidence that premenopausal African-American and Hispanic women represent a high-risk group that will benefit from identification of factors that contribute to late stage at presentation.

Figure 1: Percent of women in each race diagnosed with late stage breast cancer over time.

Citation Format: Namita Akolkar, Augustine Obirieze, Wayne Frederick, Lori Wilson. Racial differences in stage at diagnosis and survival for premenopausal breast cancer patients. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 170. doi:10.1158/1538-7445.AM2013-170

Revisiting childhood obesity: persistent underutilization of surgical intervention?

Over the last two decades, the prevalence of obesity in children ages 6 to 11 years has almost tripled, and more than tripled in teenagers. The purpose of this study is to define the characteristics of hospitalized obese children and utilization of bariatric surgery. Analysis of the 1998 to 2007 Healthcare Cost and Utilization Project Nationwide Inpatient Sample was conducted with years 2000, 2003, and 2006 substituted with the Kids' Inpatient Database dataset. Records with diagnosis of obesity were included in the analysis with major comorbidities defined as the presence of hypertension, obstructive sleep apnea, diabetes mellitus, or coronary artery disease. National estimates over a 10-year period were calculated using sampling weights. Approximately 223,700 children met the inclusion criteria, of which 20 per cent were morbidly obese, with an overall 20 per cent incidence of major comorbidity. Comorbidities were found to be significantly higher among Asian/Pacific Islander (28.3%), African-American (27.2%), and Hispanic (19.1%; P < 0.001) compared with white (15.6%) children. Only 2 per cent of morbidly obese children with major comorbidity underwent a bariatric procedure. Obesity remains a growing childhood epidemic with a disproportionate ethnic burden of comorbidities. Bariatric surgery remains a viable option and a structured guideline in children may provide equitable access across different ethnic and socioeconomic groups.

Revisiting Childhood Obesity: Persistent Underutilization of Surgical Intervention?

Over the last two decades, the prevalence of obesity in children ages 6 to 11 years has almost tripled, and more than tripled in teenagers. The purpose of this study is to define the characteristics of hospitalized obese children and utilization of bariatric surgery. Analysis of the 1998 to 2007 Healthcare Cost and Utilization Project Nationwide Inpatient Sample was conducted with years 2000, 2003, and 2006 substituted with the Kids’ Inpatient Database dataset. Records with diagnosis of obesity were included in the analysis with major comorbidities defined as the presence of hypertension, obstructive sleep apnea, diabetes mellitus, or coronary artery disease. National estimates over a 10-year period were calculated using sampling weights. Approximately 223,700 children met the inclusion criteria, of which 20 per cent were morbidly obese, with an overall 20 per cent incidence of major comorbidity. Comorbidities were found to be significantly higher among Asian/Pacific Islander (28.3%), African-American (27.2%), and Hispanic (19.1%; P < 0.001) compared with white (15.6%) children. Only 2 per cent of morbidly obese children with major comorbidity underwent a bariatric procedure. Obesity remains a growing childhood epidemic with a disproportionate ethnic burden of comorbidities. Bariatric surgery remains a viable option and a structured guideline in children may provide equitable access across different ethnic and socioeconomic groups.

Polymerase chain reaction-based tests for pan-species and species-specific detection of human Plasmodium parasites

BACKGROUND

There is still a need to improve the sensitivity of polymerase chain reaction (PCR) tests for malaria to detect submicroscopic asexual stage Plasmodium infections during the early phase and chronic, asymptomatic phase of infection when the parasite burden is very low.

STUDY DESIGN AND METHODS

The inhibitory effect of hemoglobin (Hb) on PCR limits the volume of blood that can be used in the PCR-based detection of intraerythrocytic Plasmodium parasites. We lysed red blood cells with saponin to reduce the Hb concentration in extracted nucleic acid and, as a result, significantly increased the volume of blood that can be tested by PCR. The analytical sensitivity of the PCR was determined using whole blood spiked with ring-stage Plasmodium falciparum parasites, and its clinical sensitivity by testing blood film-positive and blood film-negative samples from individuals living in an endemic area in Ghana.

RESULTS

We have developed a pan-Plasmodium PCR that detects all five human Plasmodium species with the highest analytical sensitivity of two P. falciparum parasites/mL of whole blood and species-specific PCR tests that distinguished between the five human Plasmodium species. Pan-Plasmodium PCR detected 78 of 78 (100%) blood film-positive and 19 of 101 (18.81%) blood film-negative samples from asymptomatic individuals living in Ghana. Pan-Plasmodium PCR was equally sensitive with samples collected as anticoagulated whole blood and clotted blood and in blood collected by finger stick into capillaries.

CONCLUSION

We have developed PCR tests with the highest reported sensitivity to date for pan-Plasmodium diagnosis and species-specific diagnosis and detected blood film-negative asymptomatic infections in individuals living in malaria-endemic countries.