温暖月份零售带壳牡蛎中副溶血性弧菌的定量研究

为了解温暖月份零售带壳牡蛎中副溶血性弧菌 (VP)的污染情况 ,2 0 0 3年 4～ 8月在福建省福州和厦门两地共收集带壳牡蛎 113份 ,样品分别来自水产品批发市场 (18% ) ,零售市场 (4 6 % )和饭店 (36 % )。采用Vitek鉴定系统和最可能数法进行VP的定量分析。结果显示 ,带壳牡蛎中VP密度的几何均数为 6 0MPN 10 0g ,4 1 6 %的样品VP密度低于 30MPN 10 0g的最低检出限 ,仅厦门2个样品菌量超过 2 4 0 0 0MPN 10 0g。两个地区、不同采样点和不同月份之间样品VP密度的几何均数差别均有统计学意义 (P <0 0 1)。厦门样品污染菌量高于福州 ;批发市场样品菌量最高 ;5月份样品菌量最高 ,为 14 9MPN 10 0g ,而 6～ 8月样品菌量约为 4 0MPN 10 0g。零售环节带壳牡蛎VP的检出率较高。未来应加强对生食海产品中VP污染状况的监测。     

A survey of oysters (Crassostrea gigas) in New Zealand for Vibrio parahaemolyticus and Vibrio vulnificus

A microbiological survey was conducted to determine the levels of total and pathogenic Vibrio parahaemolyticus (Vp) and Vibrio vulnificus (Vv) in Pacific oysters (Crassostrea gigas) collected from commercial growing areas in the North Island, New Zealand.The survey was intended to be geographically representative of commercial growing areas of Pacific oysters in New Zealand, while selecting the time frame most likely to coincide with the increased abundance of pathogenic vibrio species. Vp was detected in 94.8% of oyster samples examined (n = 58) with a geometric mean concentration of 99.3 MPN/g, while Vv was detected in 17.2% of oyster samples examined with a geometric mean concentration of 7.4 MPN/g. The frequency of Vp positive samples was 1.7 fold greater than reported in a study conducted three decades ago in New Zealand. Potentially virulent (tdh positive) Vp was detected in two samples (3.4%, n = 58) while no trh (another virulence marker) positive samples were detected. 16 S rRNA genotype could be assigned only to 58.8% of Vv isolates (8:1:1 A:B:AB ratio, n = 10). There was a good agreement [98.2% of Vp (n = 280) and 94.4% of Vv (n = 18) isolates] between molecular tests and cultivation based techniques used to identify Vibrio isolates and there was a significant (R² = 0.95, P < 0.001, n = 18) linear relationship between the MPN estimates by real-time PCR and cultivation. There was no significant correlation between any of the environmental parameters tested and Vp or Vv concentrations.     

福建省带壳牡蛎中副溶血性弧菌的市场调查

为了解零售带壳牡蛎中副溶血性弧菌(VP)的污染情况，2003年4月～2004年3月每月在福建省福州和厦门两地收集带壳牡蛎，样品共252份，分别来自水产品批发市场(11％)、零售市场(50％)和饭店(39％)。采用Vitek鉴定系统和最可能数(MPN)法进行VP的定性和定量分析。结果显示，带壳牡蛎VP几何平均密度为46MPN，100g，46％的试样VP密度低于30MPN/100g的最低检出限，仅厦门2个试样菌量超过104MPIN/100g。两个地区、不同采样点和不同季节之间试样vP平均密度差别均有显性。厦门试样菌量高于福州；批发市场试样菌量最高；春季试样菌量(93MPN/100g)高于其它季节(约为40MPN/100g)。研究结果可以用于估计生食牡蛎人群VP的暴露量。     

Populations of Vibrio parahaemolyticus in retail oysters from Florida using two methods

Vibrio parahaemolyticus is a naturally occurring estuarine bacterium that is often associated with gastroenteritis in humans following consumption of raw molluscan shellfish. A number of studies have investigated the environmental distribution of V. parahaemolyticus, but little is known about the levels of this organism during distribution of oysters or at the point of consumption. Duplicate samples of shellstock oysters were collected monthly (September 1997 to May 1998) from the same four restaurants and three wholesale seafood markets in the Gainesville, Fla. area and analyzed for total V. parahaemolyticus densities using two methods: a standard MPN method (BAM-MPN) and a new direct plating procedure (direct-VPAP). Both methods employed an alkaline phosphatase-labeled DNA probe (VPAP) targeting the species-specific thermolabile hemolysin (tlh) gene to confirm suspect colonies as V. parahaemolyticus. The highest monthly geometric mean V. parahaemolyticus density was observed in October of 1997 (approximately 3,000/g) with similarly high values during September and November of 1997. From December 1997 to May 1998 mean densities were generally less than 100/g, falling to approximately 10/g in February and March. A strong correlation (r = 0.78) between the direct-VPAP and BAM-MPN methods for determining V. parahaemolyticus densities in market-level oysters was observed. The direct-VPAP method was more rapid and precise while the BAM-MPN was more sensitive and may better recover stressed cells. The utilization of the VPAP probe for identification of V. parahaemolyticus sharply reduced the labor for either method compared to biochemical identification techniques used in earlier V. parahaemolyticus surveys.     

Inactivation of Vibrio parahaemolyticus and Vibrio vulnificus in oysters by high-hydrostatic pressure and mild heat

Several recent outbreaks associated with oysters have heightened safety concerns of raw shellfish consumptions, with the majority being attributed to Vibrio spp. The objective of this study was to determine the effect of high-hydrostatic pressure (HHP) followed by mild heating on the inactivation of Vibrio parahaemolyticus and Vibrio vulnificus in live oysters. Inoculated oysters were randomly subjected to: a) pressurization at 200–300 MPa for 2 min at 21 °C, b) mild heat treatment at 40, 45 or 50 °C for up to 20 min and c) pressure treatment of 200–300 MPa for 2 min at 21 °C followed by heat treatment at 40–50 °C. Counts of V. parahaemolyticus and V. vulnificus were then determined using the most probable number (MPN) method. Pressurization at 200–300 MPa for 2 min resulted in various degrees of inactivation, from 1.2 to >7 log MPN/g reductions. Heat treatment at 40 and 45 °C for 20 min only reduced V. parahaemolyticus and V. vulnificus by 0.7–2.5 log MPN/g while at 50 °C for 15 min achieved >7 log MPN/g reduction. HHP and mild heat had synergistic effects. Combinations such as HHP at 250 MPa for 2 min followed by heat treatment at 45 °C for 15 min and HHP at 200 MPa for 2 min followed by heat treatment at 50 °C for 5 min reduced both V. parahaemolyticus and V. vulnificus to non-detectable levels by the MPN method (<3 MPN/g). HHP at ≥275 MPa for 2 min followed by heat treatment at 45 °C for 20 min and HHP at ≥200 MPa for 2 min followed by heat treatment at 50 °C for 15 min completely eliminated both pathogens in oysters (negative enrichment results). This study demonstrated the efficiency of HHP followed by mild heat treatments on inactivation of V. parahaemolyticus and V. vulnificus and could help the industry to establish parameters for processing oysters.     

Depuration of live oysters to reduce Vibrio parahaemolyticus and Vibrio vulnificus: A review of ecology and processing parameters

Consumption of raw oysters, whether wild-caught or aquacultured, may increase health risks for humans. Vibrio vulnificus and Vibrio parahaemolyticus are two potentially pathogenic bacteria that can be concentrated in oysters during filter feeding. As Vibrio abundance increases in coastal waters worldwide, ingesting raw oysters contaminated with V. vulnificus and V. parahaemolyticus can possibly result in human illness and death in susceptible individuals. Depuration is a postharvest processing method that maintains oyster viability while they filter clean salt water that either continuously flows through a holding tank or is recirculated and replenished periodically. This process can reduce endogenous bacteria, including coliforms, thus providing a safer, live oyster product for human consumption; however, depuration of Vibrios has presented challenges. When considering the difficulty of removing endogenous Vibrios in oysters, a more standardized framework of effective depuration parameters is needed. Understanding Vibrio ecology and its relation to certain depuration parameters could help optimize the process for the reduction of Vibrio. In the past, researchers have manipulated key depuration parameters like depuration processing time, water salinity, water temperature, and water flow rate and explored the use of processing additives to enhance disinfection in oysters. In summation, depuration processing from 4 to 6 days, low temperature, high salinity, and flowing water effectively reduced V. vulnificus and V. parahaemolyticus in live oysters. This review aims to emphasize trends among the results of these past works and provide suggestions for future oyster depuration studies.     

Effects of electrolyzed oxidizing water treatment on reducing Vibrio parahaemolyticus and Vibrio vulnificus in raw oysters

Contamination of Vibrio parahaemolyticus and Vibrio vulnificus in oysters is a food safety concern. This study investigated effects of electrolyzed oxidizing (EO) water treatment on reducing V. parahaemolyticus and V. vulnificus in laboratory-contaminated oysters. EO water exhibited strong antibacterial activity against V. parahaemolyticus and V. vulnificus in pure cultures. Populations of V. parahaemolyticus (8.74 x 10(7) CFU/ml) and V. vulnificus (8.69 x 10(7) CFU/ml) decreased quickly in EO water containing 0.5% NaCl to nondetectable levels (> 6.6 log reductions) within 15 s. Freshly harvested Pacific oysters were inoculated with a five-strain cocktail of V. parahaemolyticus or V. vulnificus at levels of 10(4) and 10(6) most probable number (MPN)/g and treated with EO water (chlorine, 30 ppm; pH 2.82; oxidation-reduction potential, 1131 mV) containing 1% NaCl at room temperature. Reductions of V. parahaemolyticus and V. vulnificus in oysters were determined at 0 (before treatment), 2, 4, 6, and 8 h of treatment. Holding oysters inoculated with V. parahaemolyticus or V. vulnificus in the EO water containing 1% NaCl for 4 to 6 h resulted in significant (P < 0.05) reductions of V. parahaemolyticus and V. vulnificus by 1.13 and 1.05 log MPN/g, respectively. Extended exposure (> 12 h) of oysters in EO water containing high levels of chlorine (> 30 ppm) was found to be detrimental to oysters. EO water could be used as a postharvest treatment to reduce Vibrio contamination in oysters. However, treatment should be limited to 4 to 6 h to avoid death of oysters. Further studies are needed to determine effects of EO water treatment on sensory characteristics of oysters.     

Occurrence and distribution of Vibrio parahaemolyticus in retail oysters in Sao Paulo State, Brazil

Vibrio parahaemolyticus is a potentially pathogenic bacterium that occurs naturally in estuarine environments worldwide, and is often associated with gastroenteritis in humans following consumption of raw bivalve mollusks, especially raw oysters. The occurrence of total and pathogenic V. parahaemolyticus in 74 samples of raw oysters collected in restaurants, supermarkets, groceries and beach huts in Sao Paulo State, was monitored between February 2006 and January 2007. Enumeration of V. parahaemolyticus was performed according to the most probable number (MPN) procedure. Five to ten typical colonies were selected from thiosulfate-citrate-bile salts-sucrose (TCBS) agar plates for confirmation by the presence of the species-specific gene tlh and the virulence genes tdh and trh by multiplex PCR. V. parahaemolyticus was detected in 100% of samples. The densities of total V. parahaemolyticus varied from 1.78 to 6.04 log₁₀ (MPN/g), with higher densities being detected in fall and summer, and lower densities in winter (P < 0.05). There was no statistical difference among densities of V parahaemolyticus regarding the site of collection. None of the 1943 V. parahaemolyticus isolates contained tdh and/or trh. These data provide information for the assessment of exposure to V. parahaemolyticus in oysters consumed in Sao Paulo, State, Brazil.     

Use of mutant strain for evaluating processing strategies to inactivate Vibrio vulnificus in oysters.

Vibrio vulnificus is a ubiquitous marine bacterium frequently isolated from shellfish and associated with severe and often fatal disease in humans. Various control strategies to reduce the disease risk associated with V. vulnificus contamination in shellfish have been proposed. However, evaluating the efficacy of these control strategies is complicated because of the difficulty in distinguishing V. vulnificus from the high levels of background environmental Vibrio spp. The purpose of this research was to develop a model indicator V. vulnificus strain that could be readily differentiated from background microflora and used to facilitate the evaluation of processing efficacy. A spontaneous nalidixic acid-resistant strain of V. vulnificus (Vv-NA) was prepared from a wild-type parent (Vv-WT) using selective plating techniques. Vv-NA was very similar to Vv-WT with respect to biochemical characteristics, appearance on selective plating media, detection limits using most probable number and polymerase chain reaction, and growth rate. In comparative freeze inactivation studies on pure cultures, Vv-WT and Vv-NA had similar freeze inactivation profiles at -20 degrees C (conventional freezing), at -85 degrees C (cold blast freezing), and in liquid nitrogen (cryogenic freezing). In oyster homogenates artificially inoculated with Vv-NA, the organism was inactivated 95 to 99% after freezing, irrespective of freezing temperature. Thermal inactivation comparisons of pure cultures of Vv-WT and Vv-NA using the capillary tube method revealed statistically significant differences in D values at 47 degrees C (2.2 versus 3.0 min, respectively) and 50 degrees C (0.83 versus 0.56 min, respectively), but nearly identical values at 52 degrees C (0.21 versus 0.22 min, respectively). However, these D values were notably higher than those reported by other investigators and hence provided a conservative means by which to evaluate thermal inactivation. In oyster homogenates seeded with Vv-NA, D values of 1.3+/-0.09 min and 0.41+/-0.01 min were obtained at 46 degrees C and 48 degrees C, respectively. This study demonstrated that Vv-NA is readily enumerated and could be used as a surrogate for evaluating the degree of V. vulnificus inactivation provided by freezing and thermal treatments of oyster homogenates.     

Vibrio vulnificus load reduction in oysters after combined exposure to Vibrio vulnificus--specific bacteriophage and to an oyster extract component

Oysters infected with Vibrio vulnificus can present a serious health risk to diabetic, immunocompromised, and iron-deficient individuals. Numerous studies have been conducted with the goal of eliminating this organism from raw oysters. We utilized two natural oyster-associated components: pooled Vibrio vulnificus-specific bacteriophage and an extract of the eastern oyster (Crassostrea virginica) that contains an antimicrobial component we named anti-Vibrio vulnificus factor, which is bactericidal for V. vulnificus. Although each component alone can reduce V. vulnificus numbers independently, the simultaneous use of both components in an in vitro system successfully more effectively reduced V. vulnificus bacterial loads.     

High Salinity Relaying to Reduce Vibrio parahaemolyticus and Vibrio vulnificus in Chesapeake Bay Oysters (Crassostrea virginica)

Cases of Vibrio infections in the United States have tripled from 1996 to 2009 and these infections are most often associated with the consumption of seafood, particularly oysters (Crassostrea virginica). Information is needed on how to reduce numbers of Vibrio parahaemolyticus and Vibrio vulnificus in bi‐valve molluscan shellfish (for example, oysters). The purpose of this study was to evaluate the effectiveness of high salinity relaying or treatment in recirculating aquaculture systems (RASs) as methods to reduce the abundance of V. parahaemolyticus and V. vulnificus in oysters. For relaying field trials, oysters were collected from approved harvest waters, temperature abused outside under a tarp for 4 h, and then transferred to high (29 to 33 ppt.) and moderate (12 to 19 ppt.) salinities. For RAS treatment trial, oysters were transferred to 32 to 34 ppt. salinity at 15 °C. After 7, 14, 21, and in some instances 28 d, oysters were collected and analyzed for V. parahaemolyticus and V. vulnificus levels using multiplex real‐time PCR. Initial levels of V. parahaemolyticus and V. vulnificus ranged from 3.70 to 5.64 log₁₀ MPN/g, and were reduced by 2 to 5 logs after 21 to 28 d in high salinity water (29 to 34 ppt.). Oyster mortalities averaged 4% or less, and did not exceed 7%. Relaying of oysters to high salinity field sites or transfer to high salinity RAS tanks was more effective in reducing V. vulnificus compared with V. parahaemolyticus. These results suggest that high salinity relaying of oysters is more effective in reducing V. vulnificus than V. parahaemolyticus in the oyster species used in this study.     

Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999-2000: a national reconnaissance

To provide the first nationwide reconnaissance of the occurrence of pharmaceuticals, hormones, and other organic wastewater contaminants (OWCs) in water resources, the U.S. Geological Survey used five newly developed analytical methods to measure concentrations of 95 OWCs in water samples from a network of 139 streams across 30 states during 1999 and 2000. The selection of sampling sites was biased toward streams susceptible to contamination (i.e. downstream of intense urbanization and livestock production). OWCs were prevalent during this study, being found in 80% of the streams sampled. The compounds detected represent a wide range of residential, industrial, and agricultural origins and uses with 82 of the 95 OWCs being found during this study. The most frequently detected compounds were coprostanol (fecal steroid), cholesterol (plant and animal steroid), N,N-diethyltoluamide (insect repellant), caffeine (stimulant), triclosan (antimicrobial disinfectant), tri(2-chloroethyl)phosphate (fire retardant), and 4-nonylphenol (nonionic detergent metabolite). Measured concentrations for this study were generally low and rarely exceeded drinking-water guidelines, drinking-water health advisories, or aquatic-life criteria. Many compounds, however, do not have such guidelines established. The detection of multiple OWCs was common for this study, with a median of seven and as many as 38 OWCs being found in a given water sample. Little is known about the potential interactive effects (such as synergistic or antagonistic toxicity) that may occur from complex mixtures of OWCs in the environment. In addition, results of this study demonstrate the importance of obtaining data on metabolites to fully understand not only the fate and transport of OWCs in the hydrologic system but also their ultimate overall effect on human health and the environment.     

Prevalence and population analysis of Vibrio parahaemolyticus in retail aquatic products from the southern Fujian coast,China

Vibrio parahaemolyticus is one of the most hazardous pathogens causing seafood-borne diseases in the southern Fujian coast, China. From June to October 2016, a total of 250 samples were collected from retail markets in the Xiamen, Quanzhou, and Zhangzhou regions. Seventy-seven V. parahaemolyticus isolates were identified using polymerase chain reaction (PCR). Then, molecular typing was performed using repetitive extragenic palindromic-PCR (REP-PCR). The distribution of seven virulence genes was detected by PCR. In aquatic products, the prevalence of V. parahaemolyticus was 30.8%, and the prevalence of tdh⁺ and trh⁺ was 2.6 and 1.3%, respectively. The prevalence of type III secretion system-2 (T3SS2) and the ureC gene was 5.2 and 3.9%, respectively. All 77 strains and the reference strain V. parahaemolyticus ATCC 17802 were classified into seven molecular types using REP-PCR. Thus, our findings demonstrated that the prevalence of V. parahaemolyticus was severe in the southern Fujian coast and that the regulations for aquatic food safety should be strengthened.     

Variable repeat regions in the genome of Vibrio vulnificus and polymorphism in one of the loci in strains isolated from oysters

Vibrio vulnificus an estuarine bacterium is associated with severe wound infections and fatal septicemia related to consumption of raw shellfish. In this study we screened the two whole genome sequences available for V. vulnificus in GenBank for the presence of variable number of tandem repeat (VNTR) regions. Five potential VNTR loci with unit repeat size ranging from 6-7 nucleotides were identified for V. vulnificus genome. One of the loci designated Vv1 was selected to detect the repeat number present in V. vulnificus strains isolated from oyster samples in India. Twenty six of the thirty samples tested were found to be highly polymorphic for the Vv1 locus. Copy numbers for the hexanucleotide motif ranged from 4-55, giving rise to a total of 17 polymorphic groups. Our analysis, shows that different genotypic variants exist in the environment and the VNTR loci studied can be used as a marker for strain discrimination and in epidemiological study of this organism.     

Effectiveness of icing as a postharvest treatment for control of Vibrio vulnificus and Vibrio parahaemolyticus in the eastern oyster (Crassostrea virginica)

The focus of this research was to investigate the efficacy of icing as a postharvest treatment for reduction of the levels of Vibrio vulnificus and Vibrio parahaemolyticus in commercial quantities of shellstock oysters. The experiments were conducted in June and August of 2006 and consisted of the following treatments: (i) on-board icing immediately after harvest; (ii) dockside icing approximately 1 to 2 h prior to shipment; and (iii) no icing (control). Changes in the levels of pathogenic Vibrio spp. during wholesale and retail handling for 2 weeks postharvest were also monitored. On-board icing achieved temperature reductions in all sacks in accordance with the National Shellfish Sanitation Program standard, but dockside icing did not meet this standard. Based on one-way analysis of variance, the only statistically significant relationship between Vibrio levels and treatment occurred for samples harvested in August; in this case, the levels of V. vulnificus in the noniced oysters were significantly higher (P < 0.05) than were the levels in the samples iced on-board. When analyzing counts over the 14-day storage period, using factorial analysis, there were statistically significant differences in V. vulnificus and V. parahaemolyticus levels by sample date and/or treatment (P < 0.05), but these relationships were not consistent. Treated (iced) oysters had significantly higher gaping (approximately 20%) after 1 week in cold storage than did noniced oysters (approximately 10%) and gaping increased significantly by day 14 of commercial storage. On-board and dockside icing did not predictably reduce the levels of V. vulnificus or V. parahaemolyticus in oysters, and icing negatively impacted oyster survival during subsequent cold storage.     

Vibrio species involved in seafood-borne outbreaks (Vibrio cholerae,V. parahaemolyticus and V. vulnificus): Review of microbiological versus recent molecular detection methods in seafood products

Seafood products are widely consumed all around the world and play a significant role on the economic market. Bacteria of the Vibrio genus can contaminate seafood and thus pose a risk to human health. Three main Vibrio species, V. cholerae, V. parahaemolyticus and V. vulnificus, are potentially pathogenic to humans. These species are responsible for a dramatic increase of seafood-borne infections worldwide. Hence, early detection of total and pathogenic Vibrio is needed and should rely on quick and effective methods. This review aims to present the standard methods FDA-BAM, ISO/TS 21872–1:2007 and TS 21872–2:2007 and compare them to recent molecular biology methods including endpoint PCR, quantitative real-time PCR (qPCR) and PCR-derived methods with a focus on LAMP (loop-mediated isothermal amplification). The available methods presented here are dedicated to the detection and identification of the Vibrio species of interest in seafood.     

A model of the effect of temperature on the growth of pathogenic and nonpathogenic Vibrio parahaemolyticus isolated from oysters in Korea

Vibrio parahaemolyticus is recognized as the leading cause of human gastroenteritis associated with the consumption of seafood. The objective of this study was to model the growth kinetics of pathogenic and nonpathogenic V. parahaemolyticus in broth and oyster slurry. Primary growth models of V. parahaemolyticus in broth and oyster slurry fit well to a modified Gomperz equation (broth R(2)=0.99; oyster slurry R(2)=0.96). The lag time (LT), specific growth rate (SGR), and maximum population density (MPD) of each primary model were compared. The growth of nonpathogenic V. parahaemolyticus was found to be more rapid than that of pathogenic V. parahaemolyticus, regardless of the model medium. In addition, significant (P<0.05) differences in the growth kinetics between pathogenic and nonpathogenic V. parahaemolyticus in broth were observed at 10 degrees C. When compared to growth in broth, the growth of V. parahaemolyticus was delayed in oyster slurry, and growth was not observed at 10 or 15 degrees C. The Davey and square root models were identified as appropriate secondary models for predicting the LT and SGR, respectively. For the broth model, the average B(f) and A(f) values for LT were found to be 0.97 and 1.3, respectively, whereas the average B(f) and A(f) values for SGR were 1.05 and 1.11, respectively. The model generated in this study predicted an LT that was shorter and an SGR that was similar to those that were actually observed, which indicates that these models provide a reliable and safe prediction of V. parahaemolyticus growth.     

Trends in exposure to polyfluoroalkyl chemicals in the U.S. Population: 1999-2008

Since 2002, practices in manufacturing polyfluoroalkyl chemicals (PFCs) in the United States have changed. Previous results from the National Health and Nutrition Examination Survey (NHANES) documented a significant decrease in serum concentrations of some PFCs during 1999-2004. To further assess concentration trends of perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorohexane sulfonate (PFHxS), and perfluorononanoate (PFNA), we analyzed 7876 serum samples collected from a representative sample of the general U.S. population ≥12 years of age during NHANES 1999-2008. We detected PFOS, PFOA, PFNA, and PFHxS in more than 95% of participants. Concentrations differed by sex regardless of age and we observed some differences by race/ethnicity. Since 1999-2000, PFOS concentrations showed a significant downward trend, because of discontinuing industrial production of PFOS, but PFNA concentrations showed a significant upward trend. PFOA concentrations during 1999-2000 were significantly higher than during any other time period examined, but PFOA concentrations have remained essentially unchanged during 2003-2008. PFHxS concentrations showed a downward trend from 1999 to 2006, but concentrations increased during 2007-2008. Additional research is needed to identify the environmental sources contributing to human exposure to PFCs. Nonetheless, these NHANES data suggest that sociodemographic factors may influence exposure and also provide unique information on temporal trends of exposure.