亚砷酸钠对人正常肝细胞凋亡及Bax和Bcl-2 mRNA和蛋白表达的影响

目的探讨亚砷酸钠对人正常肝(L-02)细胞凋亡及Bax、Bcl-2 m RNA和蛋白表达的影响。方法将L-02肝细胞分别暴露于含0(对照)、50、100、150μmol/L亚砷酸钠的培养基中暴露24 h。采用MTT法检测L-02肝细胞的存活率,采用流式细胞术检测L-02肝细胞凋亡率,采用RT-PCR的方法检测Bax、Bcl-2 m RNA相对表达情况,采用Westernblotting方法检测L-02肝细胞中Bax、Bcl-2蛋白的表达情况。结果与对照组相比,各浓度亚砷酸钠染毒组L-02细胞的存活率均较低,凋亡率均较高,差异均有统计学意义(P0.05);且随着亚砷酸钠染毒浓度的升高,L-02细胞的存活率呈下降趋势,而凋亡率上升趋势。与对照组相比,各浓度亚砷酸钠染毒组L-02细胞中Bcl-2、Bax m RNA和蛋白的表达水平均较高,100μmol/L亚砷酸钠染毒组Bcl-2 m RNA/Bax m RNA值也较高,而150μmol/L亚砷酸钠染毒组Bcl-2 m RNA/Bax m RNA值及50、150μmol/L亚砷酸钠染毒组Bcl-2蛋白/Bax蛋白值均较低,差异均有统计学意义(P0.05)。结论亚砷酸钠可抑制L-02肝细胞的生长,诱导细胞凋亡的发生;其机制可能与Bcl-2家族的激活有关。     

氧化苦参碱对亚砷酸钠致人肝细胞损伤的拮抗作用

目的探讨氧化苦参碱(oxymatrine,OM)对亚砷酸钠致人胎肝(L-02)细胞株损伤的拮抗作用。方法将处于对数生长期的L-02细胞分别培养于0μmol/L亚砷酸钠(对照)、OM(200μg/ml)、亚砷酸钠(100μmol/L)及亚砷酸钠(100μmol/L)+OM(50、100、200μg/ml)的培养基中暴露18 h。检测细胞培养液中天冬氨酸氨基转移酶(AST)、丙氨酸氨基转移酶(ALT)的水平和细胞葡萄糖调节蛋白78(glucose regulated protein 78,GRP78)、CCAAT/增强子结合蛋白同源蛋白(CCAAT/enhancer-binding protein homologous protein,CHOP)蛋白的表达水平及细胞凋亡率。结果OM组与对照组各项指标差异均无统计学意义(P0.05)。与对照组及OM处理组比较,亚砷酸钠组细胞培养上清液中AST、ALT水平、细胞凋亡率、GRP78及CHOP蛋白表达水平显著升高(P0.05);而不同浓度OM干预后,上述指标均有不同程度下降(P0.05)。且随着OM干预浓度的升高,上述指标均呈下降趋势。结论砷可致L-02细胞损伤,OM可通过抑制L-02细胞内质网应激及减少肝细胞凋亡,从而发挥对肝细胞的保护作用。     

c-jun末端激酶在亚砷酸钠致人胚胎肝细胞损伤中的表达

目的探讨亚砷酸钠染毒对人胚胎肝(L-02)细胞中c-jun末端激酶(JNK)的变化。方法将处于对数生长期的L-02细胞分别暴露于终浓度为0(对照)、50、100、150μmol/L的亚砷酸钠溶液中培养24 h,采用四甲基偶氮唑蓝(MTT)法检测细胞生长情况,采用流式细胞术检测染毒24 h时的细胞周期及细胞凋亡率;采用蛋白杂交(Western-blot)法检测JNK及p-JNK的蛋白表达水平。结果与对照组相比,各浓度亚砷酸钠染毒组L-02细胞的存活率及G0-G1期构成比均较低,JNK、p-JNK的蛋白表达水平和S期构成比及凋亡率均较高;而G2-M期构成比在50μmol/L亚砷酸钠染毒组较低,在100、150μmol/L亚砷酸钠染毒组均较高,差异均有统计学意义(P0.05)。且随着亚砷酸钠染毒浓度的升高,L-02细胞凋亡率及JNK和p-JNK蛋白的表达水平均呈上升趋势,细胞存活率呈下降趋势。结论亚砷酸钠诱导L-02细胞凋亡可能与JNK及p-JNK表达的增加有关。     

石蒜碱诱导结肠癌HT-29 细胞凋亡机制研究

目的 探讨石蒜碱诱导结肠癌HT-29 细胞凋亡及机制。方法 不同浓度的石蒜碱处理体外结肠癌HT-29 细胞,CCK-8法检测细胞活力,流式细胞仪和Hoechst 33258染色法检测细胞凋亡;Real time PCR实验检测Caspase-3、Bcl-2和Bax的mRNA水平;Western blot方法检测Caspase-3、Bcl-2和Bax蛋白的水平。结果 48h时石蒜碱对HT-29 细胞IC50为8.878μmol/L;与对照组比较,1.25μmol/L、2.5μmol/L、5μmol/L石蒜碱能诱导细胞凋亡(P<0.05),上调Caspase-3、Bax的mRNA和Caspase-3、Bax蛋白水平,下调Bcl-2的mRNA和Bcl-2蛋白水平,差异均有统计学意义(P<0.05)。结论 石蒜碱能通过调节Caspase-3、Bcl-2、Bax的表达水平,抑制结肠癌HT-29 细胞生长,诱导细胞凋亡,具有明显的体内抗肿瘤作用。     

氧化应激在全氟辛烷磺酰基化合物诱导人胚胎肝细胞凋亡中的作用

目的探讨全氟辛烷磺酰基化合物(PFOS)致人胚胎肝(L-02)细胞凋亡的作用及其机制。方法将处于对数生长期的L-02细胞分别暴露于终浓度为0(对照)、50、100、150、200μmol/L的PFOS溶液培养24 h。采用MTT法检测细胞活性,采用流式细胞术检测细胞凋亡率,并测定细胞线粒体内活性氧(ROS)、谷胱甘肽(GSH)、丙二醛(MDA)和超氧化物歧化酶(SOD)的水平及线粒体膜电位,采用q RT-PCR法检测凋亡相关基因caspase-3、caspase-9、bax、bcl-2 m RNA的表达水平。结果与对照组比较,150、200μmol/L PFOS染毒L-02细胞的存活率均降低,而100、150、200μmol/L PFOS染毒组L-02细胞的凋亡率均增加,差异均有统计学意义(P0.05);且随着PFOS染毒浓度的升高,L-02细胞的存活率呈下降趋势,而凋亡率呈上升趋势。与对照组比较,各浓度PFOS染毒组L-02细胞内ROS和MDA水平均增加,而各浓度PFOS染毒组L-02细胞内SOD水平和100、150、200μmol/L PFOS染毒组L-02细胞内GSH水平和线粒体膜电位均较低,差异均有统计学意义(P0.05);且随着PFOS染毒浓度的升高,L-02细胞内ROS和MDA水平均呈上升趋势,而SOD、GSH水平和线粒体膜电位均呈下降趋势。与对照组比较,各浓度PFOS染毒组L-02细胞中caspase-3、caspase-9、Bax m RNA的表达水平均较高,而bcl-2、bcl-2/bax值均较低,除50μmol/L PFOS染毒组caspase-9外,差异均有统计学意义(P0.05﹚。结论在本实验剂量下,PFOS暴露可引起L-02细胞凋亡,其机制与PFOS诱导的氧化损伤和线粒体凋亡途径有关。     

亚砷酸钠对人淋巴细胞白细胞介素和穿孔素及颗粒酶B的影响

目的探讨亚砷酸钠体外染毒对人淋巴细胞白细胞介素-6(interleukin-6,IL-6)、IL-10、穿孔素(perforin,PFP)和颗粒酶B(granzyme B,Gr B)水平的影响。方法采集健康成年人外周血,密度梯度离心分离出淋巴细胞,分别暴露于含终浓度为0.00(对照)、5.00、10.00、20.00、30.00μmol/L亚砷酸钠的培养基染毒12、24、48 h。采用HE染色法鉴定染毒模型;MTT比色法检测细胞存活率;ELISA法检测IL-6、IL-10、PFP和Gr B的水平。结果与不同时间的对照组相比,5.00μmol/L亚砷酸钠染毒组淋巴细胞的存活率均升高,而10.00~30.00μmol/L亚砷酸钠染毒组淋巴细胞的存活率均降低,差异有统计学意义(P0.05)。与相同浓度亚砷酸钠染毒12 h比较,20.00、30.00μmol/L亚砷酸钠染毒24 h及10.00~30.00μmol/L亚砷酸钠染毒48 h淋巴细胞的存活率均降低,差异有统计学意义(P0.05)。与对照组相比,10.00~30.00μmol/L亚砷酸钠染毒12 h组和各浓度亚砷酸钠染毒24 h组及20.00、30.00μmol/L亚砷酸钠染毒48 h组淋巴细胞分泌的IL-6水平均较高,差异有统计学意义(P0.05)。与对照组相比,30.00μmol/L亚砷酸钠染毒12 h组和20.00、30.00μmol/L亚砷酸钠染毒24 h组及10.00~30.00μmol/L亚砷酸钠染毒48 h组淋巴细胞分泌的IL-10水平均较高,差异有统计学意义(P0.05)。与对照组相比,10.00~30.00μmol/L亚砷酸钠染毒12、24 h组及各浓度亚砷酸钠染毒48 h组淋巴细胞分泌的PFP水平均较高,差异有统计学意义(P0.05)。与相同浓度亚砷酸钠染毒12 h比较,各浓度亚砷酸钠染毒组淋巴细胞分泌的PFP水平均升高,除10.00μmol/L亚砷酸钠染毒24 h外,差异均有统计学意义(P0.05)。与对照组相比,30.00μmol/L亚砷酸钠染毒12 h组和20.00、30.00μmol/L亚砷酸钠染毒24、48 h组淋巴细胞分泌的Gr B水平均较高,差异有统计学意义(P0.05)。不同浓度亚砷酸钠染毒12、24、48 h后淋巴细胞分泌的IL-6、IL-10、Gr B水平间比较,差异均无统计学意义(P0.05)。结论砷暴露可诱导IL-6、IL-10、穿孔素及颗粒酶B表达水平升高,导致细胞因子分泌平衡紊乱,此可能在砷致免疫系统损伤中发挥重要作用。     

左卡尼汀对过氧化氢诱导血管内皮细胞氧化应激损伤的影响

目的研究左卡尼汀(L-Ca)对过氧化氢(H_2O_2)诱导人脐静脉内皮(EA.hy926)细胞氧化应激损伤的影响,为探讨L-Ca的心血管保护作用提供理论和实验依据。方法采用750μmol/L H_2O_2作用12 h建立血管内皮细胞氧化应激损伤模型。实验共分为5组:对照组、模型组(H_2O_2组)及L-Ca低、中、高剂量(0.5、1、2 mmol/L)干预组。采用CCK-8法检测细胞活力,检测细胞培养上清液中乳酸脱氢酶(LDH)含量,用Hoechst 33258荧光染色法观察细胞凋亡情况,运用Annexin V-FITC/PI双染流式细胞术分析细胞凋亡水平,qRT-PCR法分析Caspase-9、Caspase-3 mRNA转录水平;用Western blot法对Bcl-2、Bax及Cleaved Caspase-3蛋白表达水平进行分析。采用SPSS 25.0软件进行单因素方差分析和LSD-t检验。结果与对照组相比,模型组细胞活力较低,上清液LDH含量、细胞凋亡率较高,Caspase-9、Caspase-3 mRNA及Cleaved Caspase-3蛋白表达水平较高,Bcl-2/Bax蛋白比值较低;与模型组相比,L-Ca低、中、高剂量组细胞活力均明显升高,上清液LDH含量、细胞凋亡率均显著降低,Caspase-9、Caspase-3 mRNA相对表达量均明显下降,Bcl-2/Bax比值均升高,Cleaved Caspase-3蛋白表达水平均降低,且均有剂量依赖关系,差异均有统计学意义(P0.05,P0.01)。结论 L-Ca能够减轻H_2O_2对血管内皮细胞损伤,提高细胞活力,减少细胞凋亡,其机制可能与抑制Caspase-9和Caspase-3级联反应,上调Bcl-2/Bax蛋白比值有关。     

3种抗氧化剂对亚砷酸钠染毒人膀胱上皮细胞血管内皮生长因子表达的拮抗作用研究

目的探讨抗氧化剂褪黑素(melatonin,MEL)、N-乙酰半胱氨酸(N-acetyl cysteine,NAC)、维生素C(Vitamin,VC)对砷诱导人正常膀胱上皮(SV-HUC-1)细胞血管内皮生长因子(vascular endothelial growth factor,VEGF)表达的拮抗作用。方法将处于对数生长期的SV-HUC-1细胞暴露于含终浓度分别为0(对照)、0.5、1、2、4、8、10μmol/L亚砷酸钠的F12K完全培养基染毒24 h,或者含终浓度分别为4、10μmol/L亚砷酸钠的F12K完全培养基染毒0(对照)、4、12、24、48、72 h;联合暴露组在加入含终浓度分为4μmol/L亚砷酸钠的F12K完全培养基前30 min分别加入1%二甲基亚砜(DMSO)和抗氧化剂MEL、VC、NAC(终浓度分别为0.5、1、1 mmol/L),染毒24 h。分别采用Western blot法和RT-PCR法检测SV-HUC-1细胞VEGF蛋白和mRNA的表达水平。结果 10μmol/L亚砷酸钠染毒组SV-HUC-1细胞VEGF mRNA的表达水平高于对照组,差异有统计学意义(P0.05);且随着亚砷酸钠染毒剂量的升高,SV-HUC-1细胞VEGF mRNA的表达水平呈上升趋势。与对照组比较,4μmol/L亚砷酸钠染毒12、24、48 h及10μmol/L亚砷酸钠染毒24和48 h后SV-HUC-1细胞VEGF mRNA的表达水平均升高,差异有统计学意义(P0.05);且随着亚砷酸钠染毒时间的延长,各剂量组SV-HUC-1细胞VEGF mRNA的表达水平均呈先上升后下降的趋势。与对照组比较,4μmol/L亚砷酸钠+DMSO染毒组SV-HUC-1细胞中VEGF蛋白的表达水平均增加,差异有统计学意义(P0.05)。与4μmol/L亚砷酸钠+DMSO染毒组比较,亚砷酸钠+NAC染毒组SV-HUC-1细胞中VEGF蛋白的表达水平较高,差异有统计学意义(P0.05);而亚砷酸钠与MEL和VC联合染毒组SV-HUC-1细胞中VEGF蛋白的表达水平无明显改变。结论砷能诱导人正常膀胱上皮细胞VEGF表达增加,NAC能增加VEGF表达。     

赖氨酸甲基转移酶PR-Set7在亚砷酸钠致人永生化皮肤角质形成细胞DNA损伤中的作用

目的探讨组蛋白甲基转移酶PR-Set7在亚砷酸钠致人永生化皮肤角质形成细胞(Ha Ca T细胞)DNA损伤中的作用机制。方法将处于对数生长期的Ha Ca T细胞暴露于含终浓度分别为0(对照)、1.25、2.5、5、10μmol/L亚砷酸钠的DMEM高糖培养基染毒24 h。采用MTT法测定Ha Ca T细胞的存活情况。另设对照(24 h)组、亚砷酸钠(10μmol/L,24 h)染毒组、PR-Set7小干扰RNA干扰组(Si PR-Set7,50 nmol/L,48 h)和联合暴露(50 nmol/L Si PR-Set7干扰48 h后,10μmol/L亚砷酸钠暴露24 h)组。分别采用q RT-PCR法检测PR-Set7 m RNA的表达水平,采用Western blot法检测H4K20me1和PR-Set7蛋白的表达水平,采用单细胞凝胶电泳法检测DNA损伤水平。结果与对照组相比,5、10μmol/L亚砷酸钠染毒组Ha Ca T细胞的存活率均较低,差异有统计学意义(P0.05)。与对照组比较,5、10μmol/L亚砷酸钠染毒组Ha Ca T细胞PR-Set7蛋白和m RNA的表达水平均升高,而H4K20me1蛋白的表达水平降低;2.5、5、10μmol/L亚砷酸钠染毒组Ha Ca T细胞尾部DNA%及尾矩升高,差异有统计学意义(P0.05)。随着亚砷酸钠染毒浓度的升高,Ha Ca T细胞PR-Set7蛋白和m RNA的表达水平均呈上升趋势,而H4K20me1蛋白和m RNA的表达水平呈下降趋势,DNA损伤水平(尾部DNA%及尾矩)呈上升趋势。与对照组比较,Si PR-Set7干扰组Ha Ca T细胞PR-Set7蛋白的表达大幅下降;亚砷酸钠染毒组、Si PRSet7干扰组和联合暴露组Ha Ca T细胞H4K20me1蛋白的表达水平均降低,而尾部DNA%及尾矩均升高,差异有统计学意义(P0.05)。与亚砷酸钠染毒组比较,联合暴露组Ha Ca T细胞PR-Set7蛋白和m RNA以及H4K20me1蛋白的表达均降低,而Ha Ca T细胞尾部DNA%及尾矩均升高,差异有统计学意义(P0.05)。结论在对Ha Ca T细胞进行PR-Set7干扰后,亚砷酸钠可能通过抑制组蛋白甲基转移酶PR-Set7蛋白及m RNA的表达水平,从而降低H4K20me1的修饰水平,影响Ha Ca T细胞DNA损伤修复能力,使DNA损伤加重。     

六价铬对L-02肝细胞中Caspase-3与Bcl-2表达影响

为探讨六价铬对L-02肝细胞中Caspase-3与Bcl-2表达的影响,将L-02肝细胞暴露于5、10、20 μmol/L重铬酸钾溶液,在Caspase-3特异性抑制剂氟甲基酮(Z-DEVD-FMK)与Bcl-2特异性抑制剂ABT-737存在的条件下分别检测Caspase-3以及Bcl-2 mRNA的表达水平以及Caspase-3的活力.结果显示Cr(Ⅵ)处理激活Caspase-3但抑制Bcl-2;Caspase-3抑制剂缓解了Bcl-2表达的下降,Bcl-2抑制剂使原本已被激活的Caspase-3表达进一步升高.提示本实验剂量的Cr(Ⅵ)可诱导L-02肝细胞发生细胞凋亡,且Bcl-2与Caspase-3之间存在负反馈调节作用.     

Calcium intake in the elderly: validation of a dietary questionnaire

Epidemiological studies of calcium and osteoporosis have been hampered by the lack of a suitable tool for assessing calcium intake. This report describes a new frequency and amount questionnaire for measuring present and past calcium intake in the elderly. The validity of the questionnaire was tested against two commonly used standards of dietary assessment, five-day duplicate diets and seven-day weighed dietary inventories. The resulting correlation coefficients were, respectively, r = 0.76 and r = 0.69, while that for repeatability was r = 0.84. Furthermore, the questionnaire categorized subjects into thirds of the distribution of intake with almost no gross misclassification. It is suggested that the present findings may be extended to the majority of normal, healthy elderly subjects, implying wide application for the questionnaire in the assessment of calcium intake in the elderly.     

Self-reported health problems among Swedish miners one year after unemployment

Unemployment is considered to be a public health concern sincedeterioration in the health of the unemployed is often anticipated.However, for some groups, such as miners, unemployment mightimprove health due to a cessation of potentially harmful occupationalexposures. This study evaluates the health of 79 miners in oneSwedish iron-ore mine, and 226 age-matched controls from thegeneral population, during one year after the closure of themine. The participants received a questionnaire regarding medicalhistory and subjective symptoms at the beginning of the studyperiod, and after one year. Statistically significant negativeeffects on self-reported health attributable to unemploymentwere not found, although neuropsychiatric symptoms were morecommon among the unemployed miners. The miners reported a statisticallysignificant improvement in grip force (p=0.031). They had asignificantly higher prevalence of symptoms associated withmining related exposures when compared with the population controls;pain in the upper extremities [relative risk (RR)=2.27, 95%confidence interval (Cl)=1.44–3.59), back pain (RR=1.84;Cl=1.237–2.75), vasospastic disease of the fingers (RR=2.05;Cl=1.18–3.57) and obstructive respiratory symptoms (attacksof dyspnea and wheezing: RR=3.67; Cl=1.167–11.6).     

Excès de cas humains et animaux de tularémie en France au cours de l’hiver 2007–2008 : émergence ou phénomène isolé ?

Context

Tularemia is a zoonosis affecting humans and hares in France. We describe the results of surveillance in both species, in 2007 and 2008.

Methods

Human tularemia cases are mandatorily notifiable in France since 2003. In hares, surveillance relies on volunteer hunter associations in all districts of the country. Data from mandatory reports and volunteer surveillance in 2007/2008 were analyzed and compared with previous results.

Results

In 2007/2008, 144 cases were reported in humans and 117 cases in hares. This was a 100% increase compared to previous years. Human cases differed from those of previous years only by the frequency of contact with breeding animals. Human cases without any documented risk exposure were also more frequent.

Conclusion

An increase of tularemia cases occurred in 2007/2008 in both species. Complementary studies are needed to identify the species reservoir in France to understand the causes of this peak of cases.     

深圳公立医院管理体制改革制度设计

深圳公立医院管理体制改革实行政事分开、管办分开,在理事会架构下按法定机构模式组建市医管中心,落实公立医院运营管理自主权.作者从当前公立医院管理体制的弊端入手,介绍了深圳市进行公立医院管理体制改革的基本思路及改革方案设计的主要举措,深入剖析了的改革方案的特点,并对改革效果进行了预测.     

Occupational health hazards in mining: an overview

This review article outlines the physical, chemical, biological, ergonomic and psychosocial occupational health hazards of mining and associated metallurgical processes. Mining remains an important industrial sector in many parts of the world and although substantial progress has been made in the control of occupational health hazards, there remains room for further risk reduction. This applies particularly to traumatic injury hazards, ergonomic hazards and noise. Vigilance is also required to ensure exposures to coal dust and crystalline silica remain effectively controlled.     

Effects of nitrogen dioxide on red blood cells of rats: Changes in components of red cell membranes during in vivo exposure to NO2

Red cell membranes, prepared from red blood cells of rats exposed to 4, 10, or 20 ppm nitrogen dioxide (NO₂) for 1 to 10 days, were examined for evidence of changes in membrane components. Appreciable changes were not found in contents of phospholipid and cholesterol during exposure to 10 ppm NO₂. By contrast, protein content altered with the time of exposure. Moreover, changes in protein composition were observed by employing sodium dodecyl sulfate — polyacrylamide gel electrophoresis. Twenty-four-hour exposure to NO₂ at the concentration above 10 ppm resulted in a marked increase in the percentage of lysophosphatidylethanolamine (LysoPE) to the total phospholipids. The prolonged exposure to 10 ppm NO₂ gave rise to a further increase in LysoPE, whereas the percentage of phosphatidylethanolamine (PE) showed a gradual decrease. A 1-day exposure to 4.0 ppm NO₂ also caused an increase in sialic acid content and decreases in those of PE and hexose. In addition to contents of these components the percentage of LysoPE increased 5 days after exposure and the elevated values were maintained up to the end of exposure period. These results demonstrate that red blood cells in circulation exhibit different membrane properties in terms of lipid and carbohydrate composition during 10 days of exposure to 4.0 ppm NO₂.     

Manufacture and use of nanomaterials: current status in the UK and global trends

This paper provides an overview of the production and use of nanomaterials (NMs), particularly in the UK. Currently, relatively few companies in the UK are identifiable as NM manufacturers, the main emphasis being the bulk markets in metals and metal oxides, and some niche markets such as carbon nanotubes and quantum dots. NM manufacturing in the UK does not reflect the global emphasis on fullerenes, nanotubes and fibres. Some assumptions have been made about the types of NM that are likely to be imported into the UK, which currently include fullerenes, modified fullerenes and other carbon-based NMs including nanotubes. Many university departments, spin-offs and private companies have developed processes for the manufacture of NMs but may only be producing small quantities for research and development (R&D) purposes. However, some have the potential to scale up to produce large quantities. The nanotechnology industry in the UK has strong R&D backup from universities and related institutions. This review has covered R&D trends at such institutions, and appropriate information has been added to a searchable database. While several companies are including NMs in their products, only a few (e.g. manufacturers of paints, coatings, cosmetics, catalysts, polymer composites) are using nanoparticles (NPs) in any significant quantities. However, this situation is likely to change rapidly. There is a need to collect more information about exposure to NPs in both manufacturing and user scenarios. As the market grows, and as manufacturers switch from the micro- to the nanoscale, the potential for exposure will increase. More research is required to quantify any risks to workers and consumers.     

Investigating clusters in the workplace and beyond

Clusters of disease are common and occur in the workplace and in the general community. They often arouse considerable concern among the population. Investigations have sometimes lead to exciting new knowledge, but in general the investigation of clusters is difficult and often unrewarding, especially for community clusters. In the workplace, investigations are more likely to find associations and even new causes, but still many clusters remain enigmatic. Despite this, there are many reasons for investigating clusters, including allaying community concern and identifying uncontrolled exposures. A structure for investigating clusters in the workplace is suggested.