Modes of transmission for Ascaris lumbricoides and Trichuris trichiura among Chinese children in Macao City

To obtain more information on the transmission of Ascaris lumbricoides and Trichuris trichiura in Macao City, 308 Chinese children were surveyed. The infection rates of A. lumbricoides and T. trichiura were 14.9 and 6.8%, respectively. There was no association between the infections. A. lumbricoides infection was associated with age and T. trichiura with new immigrants from China. No association was found between the infections and family socio-economic factors. The results suggest that the modes of transmission for A. lumbricoides and T. trichiura may be different in highly urbanized areas.     

Strategy of Ascaris lumbricoides and Trichuris trichiura for the environmental contamination, in an endemic area

The distribution of frequencies of the number per grame of Ascaris lumbricoides and Trichuris trichiura in the faeces of naturally infected human in endemic areas, were found following a negative binomial distribution and an overdispersal pattern, independently of the ages of hosts. These results show, that only few hosts, independently of their ages, are involved in the higher environment contamination.     

Nematode infections are risk factors for staphylococcal infection in children

Nematode infection may be a risk factor for pyogenic liver abscess in children and we hypothesized that the immunomodulation induced by those parasites would be a risk factor for any staphylococcal infection in children. The present study was designed to compare, within the same hospital, the frequency of intestinal nematodes and Toxocara infection in children with and without staphylococcal infections. From October 1997 to February 1998, 80 children with staphylococcal infection and 110 children with other diseases were submitted to fecal examination, serology for Toxocara sp., evaluation of plasma immunoglobulin levels, and eosinophil counts. Mean age, gender distribution, birthplace, and socioeconomic conditions did not differ significantly between the two groups. Frequency of intestinal nematodes and positive serology for Toxocara, were remarkably higher in children with staphylococcal infections than in the non-staphylococcal group. There was a significant correlation between intestinal nematodes or Toxocara infection and staphylococcal infection in children, reinforced by higher eosinophil counts and higher IgE levels in these children than in the control group. One possible explanation for this association would be the enhancement of bacterial infection by the immunomodulation induced by helminth infections, due to strong activation of the Th2 subset of lymphocytes by antigens from larvae and adult worms.     

Prevalence and intensity of infections of Ascaris lumbricoides and Trichuris trichiura and associated socio-demographic variables in four rural Honduran communities

Between January and March 1998, a cross-sectional survey was carried out in four rural communities in Honduras, Central America. We examined the prevalence and intensity of Ascaris lumbricoides and Trichuris trichiura infections among 240 fecal specimens, and the association between selected socio-demographic variables and infection for 62 households. The overall prevalence of A. lumbricoides and T. trichiura was 45% (95% CI 39.0-51.9) and 38% (95% CI 31.8-44.4) respectively. The most intense infections for Ascaris and Trichuris were found in children aged 2-12 years old. By univariate analysis variables associated with infections of A. lumbricoides were: number of children 2-5 years old (p=0.001), level of formal education of respondents (p=0.01), reported site of defecation of children in households (p=0.02), households with children who had a recent history of diarrhea (p=0.002), and the location of households (p=0.03). Variables associated with both A. lumbricoides and T. trichiura infection included: number of children 6-14 years old (p=0.01, p=0.04, respectively), ownership of a latrine (p=0.04, p=0.03, respectively) and coinfection with either helminth (p=0.001, p=0.001, respectively). By multivariate analysis the number of children 2-5 years living in the household, (p=0.01, odds ratio (OR)=22.2), children with a recent history of diarrhea (p=0.0, OR=39.8), and infection of household members with T. trichiura (p=0.02, OR=16.0) were associated with A. lumbricoides infection. The number of children 6-14 years old in the household was associated with both A. lumbricoides and T. trichiura infection (p=0.04, p=0.01, OR=19.2, OR=5.2, respectively).     

Individual predisposition, household clustering and risk factors for human infection with Ascaris lumbricoides: new epidemiological insights

Background

Much of our current understanding of the epidemiology of Ascaris lumbricoides infections in humans has been acquired by analyzing worm count data. These data are collected by treating infected individuals with anthelmintics so that worms are expelled intact from the gastrointestinal tract. Analysis of such data established that individuals are predisposed to infection with few or many worms and members of the same household tend to harbor similar numbers of worms. These effects, known respectively as individual predisposition and household clustering, are considered characteristic of the epidemiology of ascariasis. The mechanisms behind these phenomena, however, remain unclear. In particular, the impact of heterogeneous individual exposures to infectious stages has not been thoroughly explored.

Methodology/Principal Findings

Bayesian methods were used to fit a three-level hierarchical statistical model to A. lumbricoides worm counts derived from a three-round chemo-expulsion study carried out in Dhaka, Bangladesh. The effects of individual predisposition, household clustering and household covariates of the numbers of worms per host (worm burden) were considered simultaneously. Individual predisposition was found to be of limited epidemiological significance once household clustering had been accounted for. The degree of intra-household variability among worm burdens was found to be reduced by approximately 58% when household covariates were included in the model. Covariates relating to decreased affluence and quality of housing construction were associated with a statistically significant increase in worm burden.

Conclusions/Significance

Heterogeneities in the exposure of individuals to infectious eggs have an important role in the epidemiology of A. lumbricoides infection. The household covariates identified as being associated with worm burden provide valuable insights into the source of these heterogeneities although above all emphasize and reiterate that infection with A. lumbricoides is inextricably associated with acute poverty.     

Intestinal parasitic infections and risk factors for infection in Kenyan children with and without HIV infection

It has been reported that HIV infection is not a risk factor for Entamoeba species infection but is for Giardia intestinalis assemblage B in children living in Western Kenya. This study aimed to investigate the prevalence of and the risk factors for Entamoeba spp. and G. intestinalis infection in children living in Nairobi, Kenya. This cross-sectional study included 87 children with HIV [HIV(+)] and 85 without HIV [HIV(−)]. Stool and blood samples were collected for the detection of the parasites by PCR and immunological analyses using flow cytometry. Sociobehavioral and hygienic data were collected using questionnaires and analyzed statistically. The prevalence of Entamoeba spp. infection was significantly lower in the HIV(+) than in the HIV(−) children (63.2% vs. 78.8%, P = 0.024), whereas the prevalence of G. intestinalis infection was not (27.6% vs. 32.9%, P = 0.445). “Not boiling drinking water” (adjusted odds ratio [aOR]: 3.8, P = 0.044) and “helping in nursery care” (aOR: 2.8, P = 0.009) were related to G. intestinalis assemblage B infection, and “CD4/CD8 ratio ≥1” was related to Entamoeba spp. infection (aOR: 3.3, P = 0.005). In stratified regression analyses, HIV infection was negatively associated with G. intestinalis assemblage B infection in females (aOR: 0.3, P = 0.022), but positively associated in males (aOR 3.8, P = 0.04). These results suggest that G. intestinalis assemblage B infection is related to hygienic conditions, while Entamoeba spp. infection is an indicator of better immunological status, and that the role of HIV infection in Giardia infection may differ between Kenyan boys and girls.     

T-helper 17-related cytokines and IgE antibodies during hepatitis A virus infection in children

We determined the serum IgE levels and T-helper (Th)17-related cytokines duringdistinct hepatitis A virus (HAV)-induced clinical courses in children. Asignificantly higher concentration of macrophage inflammatory protein 3α, interleukin(IL)-17E and IL-17F in HAV-infected children with intermediate liver injury comparedwith those with minor liver damage was found. A reduction in the IgE levels in thosepatients who showed the highest levels of IL-17F in the group of intermediate liverinjury was found. The data suggested that the Th17-related profile is associated withthe severity of HAV infection and might play a role on the modulation achieved by HAVduring allergies.     

The usefulness of casein-specific IgE and IgG4 antibodies in cow's milk allergic children

Background

Cow's milk allergy is one of the most common food allergies among younger children. We investigated IgE antibodies to milk, and IgE and IgG4 antibodies to casein, ??-lactalbumin and ??-lactoglobulin in cow's milk allergic (CMA) and non-allergic (non-CMA) children in order to study their clinical usefulness.

Methods

Eighty-three children with suspected milk allergy (median age: 3.5 years, range: 0.8-15.8 years) were diagnosed as CMA (n = 61) or non-CMA (n = 22) based on an open milk challenge or convincing clinical history. Their serum concentrations of allergen-specific (s) IgE and IgG4 antibodies were measured using ImmunoCAP^?. For the sIgG4 analysis, 28 atopic and 31 non-atopic control children were additionally included (all non-milk sensitized).

Results

The CMA group had significantly higher levels of milk-, casein- and ??-lactoglobulin-sIgE antibodies as compared to the non-CMA group. The casein test showed the best discriminating performance with a clinical decision point of 6.6 kU_A/L corresponding to 100% specificity. All but one of the CMA children aged > 5 years had casein-sIgE levels > 6.6 kU_A/L. The non-CMA group had significantly higher sIgG4 levels against all three milk allergens compared to the CMA group. This was most pronounced for casein-sIgG4 in non-CMA children without history of previous milk allergy. These children had significantly higher casein-sIgG4 levels compared to any other group, including the non-milk sensitized control children.

Conclusions

High levels of casein-sIgE antibodies are strongly associated with milk allergy in children and might be associated with prolonged allergy. Elevated casein-sIgG4 levels in milk-sensitized individuals on normal diet indicate a modified Th2 response. However, the protective role of IgG4 antibodies in milk allergy is unclear.     

The prevalence of wheezing and its association with serum zinc concentration in children and adolescents in Brazil

ObjectiveTo assess the influence of zinc serum status on the prevalence of wheezing in a sample of children and adolescents in Northeastern Brazil.Research methods and proceduresThis is a cross-sectional study which included 592 students of 6–12 years old, from the public elementary schools of São Francisco do Conde, Bahia, Northeastern Brazil. Report of wheezing in the past 12 months was collected using a questionnaire of the International Study of Asthma and Allergies in Childhood Program (ISAAC) phase III, adapted to Portuguese. The determination of serum Zn levels was performed using a flame atomic absorption spectrometer. Data on anthropometric status, level of physical activity, pubertal development and socioeconomic information, for each participant were obtained. Multivariate logistic regression analyses were used to assess the associations of interest.ResultsOf the students, 8.6% (95% CI 6.30–10.9) reported having wheezing. The mean (SD) serum zinc level was 114 (22.9 μg/dL). The results of the multiple logistic regression analysis showed, after adjustments, positive and significant association between low serum zinc levels and wheezing. Students categorized as being below the median for serum Zn concentration presented an almost 1.9-fold increase in the wheezing prevalence ratio (OR = 1.9; 95% CI 1.03–3.53).ConclusionThe main findings of this study suggest that the level of zinc may influence the risk of wheezing in late childhood on the study population.     

People with multiple tattoos and/or piercings are not at increased risk for HBV or HCV in The Netherlands

Background

Although published results are inconsistent, it has been suggested that tattooing and piercing are risk factors for HBV and HCV infections. To examine whether tattooing and piercing do indeed increase the risk of infection, we conducted a study among people with multiple tattoos and/or piercings in the Netherlands who acquired their tattoos and piercings in the Netherlands and/or abroad.

Methods

Tattoo artists, piercers, and people with multiple tattoos and/or piercings were recruited at tattoo conventions, shops (N = 182), and a biannual survey at our STI-outpatient clinic (N = 252) in Amsterdam. Participants were interviewed and tested for anti-HBc and anti-HCV. Determinants of HBV and HCV infections were analysed using logistic regression analysis.

Results

The median number of tattoos and piercings was 5 (IQR 2–10) and 2 (IQR 2–4), respectively. Almost 40% acquired their tattoo of piercing abroad. In total, 18/434 (4.2%, 95%CI: 2.64%–6.46%) participants were anti-HBc positive and 1 was anti-HCV positive (0.2%, 95%CI: 0.01%–1.29%). Being anti-HBc positive was independently associated with older age (OR 1.68, 95%CI: 1.03–2.75 per 10 years older) and being born in an HBV-endemic country (OR 7.39, 95%CI: 2.77–19.7). Tattoo- and/or piercing-related variables, like having a tattoo or piercing in an HBV endemic country, surface percentage tattooed, number of tattoos and piercings etc., were not associated with either HBV or HCV.

Conclusions

We found no evidence for an increased HBV/HCV seroprevalence among persons with multiple tattoos and/or piercings, which might be due to the introduction of hygiene guidelines for tattoo and piercing shops in combination with the low observed prevalence of HBV/HCV in the general population. Tattoos and/or piercings, therefore, should not be considered risk factors for HBV/HCV in the Dutch population. These findings imply the importance of implementation of hygiene guidelines in other countries.     

Seroprevalence and risk factors for Helicobacter pylori infection in Greenlanders

BACKGROUND: In contrast to most populations worldwide, the incidence of gastric cancer increases among Inuit in Greenland. Contributing factors to this increase are unknown, but Helicobacter pylori may be involved. However, little is known regarding the epidemiology of H. pylori in Arctic communities. With the aim of determining age-specific prevalence, risk factors, and association with clinical conditions of H. pylori infection, we carried out a population-based study of H. pylori in Sisimiut, the second biggest town of Greenland. MATERIALS AND METHODS: A population-based sample of 685 persons had serum drawn that was analyzed for H. pylori IgG antibodies using enzyme-linked immunosorbent assay (ELISA). Risk factors analyses were carried out using multivariate logistic regression models. RESULTS: The seroprevalence was lowest among children aged 0-4 years (6%), but increased rapidly thereafter. In persons aged 15-87 years the seroprevalence had stabilized around 58%. Total number of children in household, number of older, but not younger, siblings and narrow age gap to closest older sibling were associated with H. pylori seropositivity. In contrast, number of adults in household and socioeconomic status did not influence serostatus. CONCLUSIONS: The age-specific prevalence pattern in Greenland is intermediate between that of developing and developed countries. The risk factor pattern indicates crowding and older siblings in particular to be key elements in risk of infection.     

The presence in serum of proteins which are immunologically cross-reactive with Tamm-Horsfall glycoprotein.

Affinity chromatography, with rabbit anti-(human Tamm-Horsfall glycoprotein) IgG, was applied to the isolation from normal human serum of protein, which is immunologically cross-reactive with the urinary glycoprotein. The antigen-antibody complex was dissociated with the use of sodium thiocyanate solution, a medium which fails to dissociate urinary Tamm-Horsfall glycoprotein-antigen complex. The cross-reactive serum proteins were isolated in amounts of 19-24 mg/l of serum. They have apparent molecular weights, assessed by disc-gel electrophoresis in the presence of sodium dodecyl sulphate, of 125 000, 84 000 and 74 000 respectively, with mobilities differing from that of urinary Tamm-Horsfall glycoprotein. They have a much lower immunoreactivity towards the antibody than does the urinary glycoprotein. Tamm-Horsfall glycoprotein could not be demonstrated in normal serum by the techniques used. The implications of these findings are discussed in terms of pathology involving Tamm-Horsfall glycoprotein.     

Age of appearance of IgG, IgM, and IgE antibodies specific for Loa loa in Gabonese children

IgG, IgM, and IgE antibodies against the filaria Loa loa were measured in umbilical cord blood and in blood from young Gabonese children by an ELISA technique using a homologous metabolic antigen. For children in eight consecutive age groups and adults the percentage of the population positive for each of the antibody classes was determined. The number of children with maternal IgG decreased until one year of age when new synthesis began to become apparent. IgM antibodies were detected only after six months, probably indicating an early infancy as opposed to a fetal infection. The percentage of individuals positive for IgM or IgE reached a peak between two and three years old, followed by a slight decline. Over half of the individuals over one year of age had IgM antibody against L. loa, indicating long-term synthesis of this class of immunoglobulin in many people. In the first two years of life, IgE antibodies were usually accompanied by L. loa-specific IgM. This specific IgE did not appear to trigger the synthesis of nonspecific IgE. By the age of two, 95% of the population had some antibodies against L. loa and by five the percentage of individuals positive for each antibody class had reached adult levels.     

浅谈眼科手术室患者感染危险因素及防控措施

目的 分析眼科手术室患者感染危险因素,讨论感染风险管理对策。方法 回顾2017年7月至2018年8月我院眼科手术室患者的感染情况,分析感染危险因素并制定应对策略。结果 2017年7月至2018年8月我院共实施眼科手术1 987只眼,均未发生感染。空气污染,医疗器械污染,防控意识薄弱可能是患者发生感染的危险因素。结论 规范流程可以有效规避眼科手术感染,注重细节管理是预防眼科手术感染的关键。     

Prevalence and risk factors for Helicobacter pylori infection in Chinese populations

Background:  The prevalence of Helicobacter pylori is higher in developing countries. The aim of this study was to investigate the prevalence and risk factors of H. pylori infection in areas with high prevalence of gastric cancer in Jiangsu Province, China.
Methods:  A prospective epidemiologic survey of H. pylori infection was accomplished in a natural population of 1457 individuals in Xiangshui and Gaoyou counties, Jiangsu Province, China. Questionnaires and laboratory tests for H. pylori infection (¹³C-urea breath test and serum IgG antibodies to H. pylori ) were used and performed, respectively.
Result:  Among 1371 subjects who completed questionnaires and H. pylori detection, 851 (62%) were H. pylori positive. The prevalence reached a peak at the age of 30–40 years (67%). There was no sex difference. The annual family income level was shown to be positively correlated with the risk of H. pylori infection. The prevalence of H. pylori infection was also associated with family size, education level, and several diet-related factors, such as the number of times cooked rice and potatoes eaten per week, and a family history of stomach diseases. Compared to nonsymptomatic individuals, people with dyspeptic symptoms (nausea, vomiting, and belching) presented a low prevalence of H. pylori infection. No association between H. pylori prevalence and smoking or drinking was found. Using multivariate logistic regression analysis, annual family income and education level were the independent predictors for H. pylori infection.
Conclusion:  High prevalence of H. pylori infection was found in areas with a high risk of gastric cancer and was related to several risk factors. The underlying mechanisms need to be further investigated.     

老年期精神病患者多重耐药菌感染的危险因素分析

目的了解老年期精神病患者多重耐药菌感染与危险因素的相关性,为临床对老年期精神病患者合理应用抗菌药物及有效控制多重耐药菌感染提供理论依据。方法收集在2012—2014年期间嘉兴市康慈医院接受治疗的年龄在60岁以上的老年期精神病患者体内分离确认的多重耐药菌株共74株,采用SPSS 17.0统计软件做多因素Logistic回归分析,分析老年期精神病患者多重耐药菌感染的相关危险因素。结果老年期精神病患者多重耐药菌感染的单因素分析显示年龄(P=0.010)、住院时间(P=0.002)、基础疾病(P=0.188)、侵入性操作(P=0.000)、抗菌药物使用(P=0.000)、抗精神病药使用(P=0.191)等均为老年期精神病患者多重耐药菌感染的相关因素。多因素Logistic回归分析显示基础疾病和侵入性操作是老年期精神病患者多重耐药菌感染的高危险因素。结论基础疾病和侵入性操作是老年期精神病患者多重耐药菌感染的高危险因素。提示临床严防抗菌药物过度应用,减少侵入性操作,从而避免老年期精神病患者感染菌株中多重耐药菌株的产生。     

Prevalence of and risk factors for quinolone-resistant Neisseria gonorrhoeae infection in Ontario

Background

Quinolone-resistant Neisseria gonorrhoeae has swiftly emerged in Canada. We sought to determine its prevalence in the province of Ontario and to investigate risk factors for quinolone-resistant N. gonorrhoeae infection in a Canadian setting.

Methods

We used records from the Public Health Laboratory of the Ontario Agency for Health Protection and Promotion in Toronto, Ontario, and the National Microbiology Laboratory in Winnipeg, Manitoba, to generate epidemic curves for N. gonorrhoeae infection. We extracted limited demographic data from 2006 quinolone-resistant N. gonorrhoeae isolates and from a random sample of quinolone-susceptible isolates. We also extracted minimum inhibitory concentrations for commonly tested antibiotics.

Results

Between 2002 and 2006, the number of N. gonorrhoeae infections detected by culture decreased by 26% and the number of cases detected by nucleic acid amplification testing increased 6-fold. The proportion of N. gonorrhoeae isolates with resistance to quinolones increased from 4% to 28% over the same period. Analysis of 695 quinolone-resistant N. gonorrhoeae isolates and 688 quinolone-susceptible control isolates from 2006 showed a higher proportion of men (odds ratio [OR] 3.1, 95% confidence interval [CI] 2.3–4.1) and patients over 30 years of age (OR 3.1, 95% CI 2.4–3.8) in the quinolone-resistant group. The proportion of men who have sex with men appeared to be relatively similar in both groups (OR 1.4, 95% CI 1.1–1.8). Quinolone-resistant strains were more resistant to penicillin (p < 0.001), tetracycline (p < 0.001) and erythromycin (p < 0.001). All isolates were susceptible to cefixime, ceftriaxone, azithromycin and spectinomycin.

Interpretation

During 2006 in Ontario, 28% of N. gonorrhoeae isolates were resistant to quinolones. Infections in heterosexual men appear to have contributed significantly to the quinolone resistance rate. Medical practitioners should be aware of the widespread prevalence of quinolone-resistant N. gonorrhoeae and avoid quinolone use for empiric therapy.After declining for a number of years, Neisseria gonorrhoeae infections are once more on the rise in Canada. Between 1997 and 2007, reported incidence of the disease more than doubled, from 15 to 35 cases per 100 000.¹ To address the emergence of quinolone-resistant N. gonorrhoeae strains, the empiric treatment regimens for N. gonorrhoeae infection were recently revised in the 2006 Canadian Guidelines on Sexually Transmitted Infections.^2,3 Quinolones are no longer recommended for empiric therapy for N. gonorrhoeae infection.³In Canada, quinolone resistance in N. gonorrhoeae isolates increased from an estimated 2% in 2001 to 16% in 2005.⁴ Demographic risk factors for quinolone-resistant N. gonorrhoeae infection have not been studied. American studies have associated quinolone-resistant N. gonorrhoeae infection with men who have sex with men,^5,6 antibiotic use,^5,7 age above 35 years,⁵ HIV infection⁵ and travel to Asia.⁶ Public health data from the provinces of Quebec⁸ and Alberta² have also suggested an association between quinolone-resistant infection and men who have sex with men. In this study we generated epidemic curves for N. gonorrhoeae and quinolone-resistant N. gonorrhoeae infection in the province of Ontario. We also investigated demographic risk factors for quinolone-resistant N. gonorrhoeae infection.     

Reproduction and nutritional stress are risk factors for Hendra virus infection in little red flying foxes (Pteropus scapulatus)

Hendra virus (HeV) is a lethal paramyxovirus which emerged in humans in 1994. Poor understanding of HeV dynamics in Pteropus spp. (flying fox or fruit bat) reservoir hosts has limited our ability to determine factors driving its emergence. We initiated a longitudinal field study of HeV in little red flying foxes (LRFF; Pteropus scapulatus) and examined individual and population risk factors for infection, to determine probable modes of intraspecific transmission. We also investigated whether seasonal changes in host behaviour, physiology and demography affect host-pathogen dynamics. Data showed that pregnant and lactating females had significantly higher risk of infection, which may explain previously observed temporal associations between HeV outbreaks and flying fox birthing periods. Age-specific seroprevalence curves generated from field data imply that HeV is transmitted horizontally via faeces, urine or saliva. Rapidly declining seroprevalence between two field seasons suggests that immunity wanes faster in LRFF than in other flying fox species, and highlights the potentially critical role of this species in interspecific viral persistence. The highest seroprevalence was observed when animals showed evidence of nutritional stress, suggesting that environmental processes that alter flying fox food sources, such as habitat loss and climate change, may increase HeV infection and transmission. These insights into the ecology of HeV in flying fox populations suggest causal links between anthropogenic environmental change and HeV emergence.     

Trichinella spiralis: Generation in the presence of rat serum of factors chemotactic for rat cells

Chemotaxis of rat peritoneal cells, of which the eosinophil was the predominant migratory cell type, toward incubates of Trichinella spiralis was studied using a modified Boyden chamber. Excysted muscle larvae, preadults, and adults were incubated in a buffered medium for 20 hr at 37 C. Worms were incubated alone or with serum or spleen cells, or both, from immune and nonimmune rats. Incubates of worm stages alone possessed no chemotactic activity as compared with incubation medium as a negative control and zymosan-activated serum as a positive control. Both normal and immune sera tested alone stimulated cell migration to the same degree. Incubates of spleen cells from either normal or immunized hosts did not show chemotactic activity. Chemotaxis caused by normal and immune sera were not altered by incubation with homologous spleen cells. Addition of larva, preadults, and adult worms to sera, however, enhanced chemotactic activity over sera alone. Chemotaxis caused by larvae plus immune sera was significantly greater than that stimulated by larvae plus normal sera. This difference decreased when preadults were substituted for larvae and was not observed when adult worms were used. Reversal of the chemical gradients showed that active cell migration caused by various incubates was due to Chemotaxis.