A venue-based method for sampling hard-to-reach populations.

Constructing scientifically sound samples of hard-to-reach populations, also known as hidden populations, is a challenge for many research projects. Traditional sample survey methods, such as random sampling from telephone or mailing lists, can yield low numbers of eligible respondents while non-probability sampling introduces unknown biases. The authors describe a venue-based application of time-space sampling (TSS) that addresses the challenges of accessing hard-to-reach populations. The method entails identifying days and times when the target population gathers at specific venues, constructing a sampling frame of venue, day-time units (VDTs), randomly selecting and visiting VDTs (the primary sampling units), and systematically intercepting and collecting information from consenting members of the target population. This allows researchers to construct a sample with known properties, make statistical inference to the larger population of venue visitors, and theorize about the introduction of biases that may limit generalization of results to the target population. The authors describe their use of TSS in the ongoing Community Intervention Trial for Youth (CITY) project to generate a systematic sample of young men who have sex with men. The project is an ongoing community level HIV prevention intervention trial funded by the Centers for Disease Control and Prevention. The TSS method is reproducible and can be adapted to hard-to-reach populations in other situations, environments, and cultures.

Failure to learn human immunodeficiency virus test results in Los Angeles public sexually transmitted disease clinics.

BACKGROUND: Early human immunodeficiency virus (HIV) defection is essential for initiating treatment and partner-notification activities. Sexually transmitted disease (STD) clinic attendees are at high risk for infection and should be made aware of their HIV status. GOAL: To determine the characteristics associated with not receiving an HIV test result in an STD clinic setting. STUDY DESIGN: Confidential HIV testing was offered to 6,705 persons attending four public STD clinics in Los Angeles who submitted blood for syphilis serology and were tested for HIV antibody in an unlinked HIV serosurvey. Human immunodeficiency virus test results and return status were anonymously linked to other risk information. RESULTS: Only one-third of attendees were tested and given their results. Those testing HIV positive in the anonymous survey and those requesting HIV testing were most likely to receive a test result (i.e., 41% and 49%, respectively). Those solely requesting an STD examination, repeat testers, and African-Americans were least likely to receive a result (i.e., 32%, 30%, and 26%, respectively). CONCLUSIONS: Most STD clinic patients fail to receive an HIV test result. Other strategies, such as rapid HIV testing, are needed to increase participation and receipt of HIV test results in this high-risk population.

A probability-based approach for predicting HIV infection in a low prevalent population of injection drug users.

This article proposes a method for estimating HIV risk in low-HIV-prevalent populations. Allard's risk probability model was used to compute individual risk scores. Based on a sample of 3854 injection drug users (IDUs) who were confidentially tested for HIV at five methadone treatment clinics in Los Angeles County, the following self-reported risk behaviors were used to derive an individual IDU risk score: (i) frequency of injection, (ii) frequency of using uncleaned needles, (iii) number of people sharing a needle, (iv) frequency of needle sharing, and (v) type of needle sharing practice. The overall HIV prevalence for the IDU sample was 2%. The risk score was strongly associated with HIV seropositivity (chi-square = 16.1, p < 0.0001), but only one of the individual IDU risk behaviors (needle cleaning) was significantly associated with HIV seropositivity (chi-square = 10.9, P < 0.001). In addition, the risk score was strongly associated with HIV serostatus for both males and females. For females, however, none of the individual IDU risk behaviors were associated with HIV serostatus. Our findings indicate that when predicting HIV infection in a low-prevalence population, the probability-based risk score makes a statistically significant contribution over individual IDU risk behaviors.

Reasons for HIV antibody test refusal in a heterosexual sexually transmitted disease clinic population.

OBJECTIVE: To evaluate acceptance of confidential HIV antibody testing and reasons for test refusal among heterosexual clients of Los Angeles County sexually transmitted disease (STD) clinics. METHODS: From January 1993 through June 1994, all blood specimens routinely collected for syphilis serology were tested blindly for HIV antibody at seven STD clinics. Patients were counseled and offered a confidential HIV test. Rate of refusal of confidential testing and primary reason for test refusal were examined by demographic group and HIV serostatus, as determined in the blinded survey, for all heterosexual clients. RESULTS: Of 20,125 persons offered confidential testing, 35.6% refused the test. Test refusal was higher among men (38.7%) than women [31.1%; adjusted odds ratio (OR), 1.4; 95% confidence interval (CI), 1.3-1.4] and among blacks (38.6%) than whites (28.6%; adjusted OR, 1.7; 95% CI, 1.5-2.0). The most common reason for refusal was 'already know my HIV status' (40.6%), followed by 'don't want to know' (23.9%), and 'not at risk' (19.4%). Confidentiality concerns were cited as the primary reason for refusal by 2.2%. Among the 180 (0.9%) persons who tested positive in the blinded survey, 99 (55.0%) refused the confidential test. Of the 44 seropositive persons who refused the confidential test because they "already knew their HIV status', 29 (65.9%) reported their previous test to be negative. CONCLUSIONS: Efforts are needed to increase acceptance of confidential HIV testing in this heterosexual population and should (1) include a client-centered counseling approach that facilitates accurate self-assessment of risk and addresses the misperception that a prior negative test result implies an absence of risk, and (2) highlight the potential benefits of early intervention medical and psychosocial services.

Occupational risk of acquiring HIV infection through needlestick injuries.

Accidental needlestick exposures occur frequently among hospital personnel and account for most incidents of percutaneous injuries. Even if universal precautions were followed routinely, it is unlikely that multiple needlestick exposures could be avoided completely. Despite the likelihood of persons incurring multiple needlestick exposures, relatively little information is available on the cumulative risk of human immunodeficiency virus (HIV) infection for health care workers attending unrecognized HIV-infected patients. A quantitative method to estimate annual cumulative risk from multiple exposures is offered, and the risk of HIV infection is estimated by use of a probability model for health care workers in both hospital and emergency department settings.

An outbreak of furunculosis among high school athletes.

Furuncles (boils) are common among teenagers; however, few outbreaks have been documented. We investigated an outbreak of furuncles that occurred among male athletes of a Kentucky high school during the 1986 to 1987 school year. The overall attack rate was 25% (31/124). The risk of developing a furuncle increased two to three times in those who had skin injury. Athletes who sustained abrasions more than twice per week (P less than 0.01), who had a cut that required bandaging (P = 0.01), or had an unspecified injury causing a missed practice or game (P = 0.04) were at increased risk. The risk of developing furunculosis did not appear to be related to contact with formites, but rather, to contact with furuncles. Although athletes shared common areas (showers, locker rooms, practice areas, the attack rates for varsity football (36%) and varsity basketball (33%) were four times greater than for nonvarsity teams (P less than 0.01). Players who had a friend with a furuncle were more than twice as likely to also have had a furuncle (P less than 0.01). Exposure to furuncles appeared to increase the risk of furunculosis independently of reported skin injury. Control and prevention should, therefore, focus on both reducing skin injury and reducing exposure to furuncles, rather than attempting to sterilize inanimate objects.

Major histocompatibility complex control of NK-related allogeneic lymphocyte cytotoxicity in rats. The contributions of strong and medial transplantation antigens.

Allogeneic lymphocyte cytotoxicity (ALC) describes the elimination of allogeneic lymphocytes in vivo by an NK-related activity. There is evidence that ALC is demonstrable between donor and recipient when these are incompatible at MHC gene loci alone. Since ALC is a property of T cell-deficient nude rats, the role of the MHC in this rejection process needs further study. We have determined the contribution of the MHC to ALC using congenic and recombinant rats. In our analysis we have assumed that ALC involves the recognition of classic alloantigens by clonally distributed effector cells as for other examples of transplant rejection, although this is not yet proved. Strong ALC was measured between congenic rats that differed for MHC genes only. Non-MHC incompatibility alone did not elicit ALC. In the presence of MHC incompatibility the strength of ALC generated in a recipient was dependent on non-MHC genes. The PVG background generated high ALC responses whereas ALC was not measured in the DA rat. However ALC was measured in the congenic PVG-RT1avl (DA) rat. The contributions of classic class I (RT1.A), class II (RT1.B/D), and medial transplantation (RT1.C) regions of the rat MHC were determined by comparing different recombinant donors into the same recipient strain. Single region differences alone in any of these three MHC regions did not elicit full ALC. In two sets of transfers a combination of RT1.B/D and RT1.C region incompatibility was sufficient to generate a full allogeneic response. It can be concluded that the controlling element for allogeneic lymphocyte cytotoxicity is in the RT1.B/D-RT1.C region of the rat MHC.

The stable and permanent expansion of functional T lymphocytes in athymic nude rats after a single injection of mature T cells.

Athymic nude rats (PVG.rnu/rnu) were injected at 6 to 10 wk of age with 1 to 200 million thoracic duct lymphocytes (TDL) containing 40 to 60% mature T cells. Thereafter TDL-injected nude recipients were monitored for evidence of T cell function for up to 2 yr. W3/25+ T helper (Th) cells in lymph nodes (LN) increased from 7% at 2 wk to 30% at 8 wk after TDL transfer. The percent of W3/25+ cells remained elevated for the life of the recipient (up to 2 yr), approximating normal levels. The total size of the recirculating pool expanded in TDL-injected nude rats to reach 2/3 the level of euthymic controls by 16 wk, an increase of 10-fold to 15-fold in W3/25+ cells. The expansion of the W3/25+ population was independent of initial TDL dose. With time spleen and LN acquired a normal histological appearance including the development of germinal centres and a marked increase in cellularity in T cell traffic areas. TDL-injected nude rats rejected skin allografts with near normal kinetics. In addition graft vs host (GVH) responsiveness, assessed by the popliteal LN assay, progressively increased reaching a level 9 mo to 1 yr after replacement that resembled the GVH activity in euthymic controls.

The effects of interferon on the recirculation of lymphocytes in the rat.

Lymphocytes from the thoracic duct (TDL) were incubated with interferon (IFN) prior to i.v. injection into syngeneic or allogeneic recipient rats. The effect of IFN treatment on the ability of lymphocytes to migrate was studied using 'standard' TDL collected overnight at 4 degrees or an 'optimal' collection of passaged TDL which recirculate with an accelerated tempo (Smith & Ford, 1983). Interferon treatment resulted in an increase in early (30 min) localization of both standard and optimal TDL into lymph nodes. Entry of standard IFN-treated TDL was increased by 91% and 54% in cervical and mesenteric lymph nodes, respectively; increases of 50% and 22% in the same lymph nodes were recorded for optimal IFN-treated TDL. Enhanced entry of standard TDL was contrasted with a reduced ability of IFN-treated TDL to migrate out of lymph nodes; there was a reduced output into the thoracic duct and a surplus of IFN-treated lymphocytes in cervical lymph nodes despite 24 hr continuous thoracic duct drainage. Incubation with interferon did not, however, alter the ability of optimal TDL to reach the thoracic duct rapidly after injection. Allogeneic lymphocytes, which are eliminated soon after injection by an NK-like cytotoxicity, a phenomenon termed ALC, were unaffected by incubation with interferon, thus IFN-treated allogeneic lymphocytes were killed after i.v. injection as rapidly as untreated cells.

The carriage and delivery of substances to lymphatic tissues by recirculating lymphocytes. II. Long-term selective irradiation of the spleen and lymph nodes by deposition of indium-114m.

Recirculating lymphocytes were used to carry an isotope of indium, In-114m. The isotope has a half-life of 50 days, and emits both gamma and beta particles, properties that may be useful clinically. In-114m-labelled rat thoracic duct lymphocytes (TDL), injected intravenously, migrated to traffic areas in spleen and lymph nodes. The radioactivity was transferred selectively to a resident, radioresistant phagocytic population located within the marginal zone and red pulp of spleen, where it remained for at least 6 weeks. That the isotope was relatively concentrated in traffic areas, but not elsewhere, suggested that In-114m-TDL could be used as a means of producing total lymphoid irradiation without damaging bone marrow. Recipients of In-114m-TDL developed a profound lymphocytopenia within 2-3 weeks of injection but gained weight at a comparable rate to control rats. The effect of In-114m-TDL injection was also examined in rats injected with a rapidly growing, malignant rat leukaemia. In-114m-TDL delayed the onset of the proliferative phase of the leukaemia from 10 days to 20 days in a dose-dependent fashion. Repeated weekly injections of In-114m-TDL prevented the onset of the leukaemia until the injections ceased after 11 weeks. The potential use of In-114m-labelled lymphocytes in diagnosis (by external imaging) or in treatment (by localized lymphoid irradiation) is considered.

The host component of the popliteal lymph node graft-versus-host reaction. Selective representation of lymphocyte subsets and the requirement for alloantigenic incompatibility between donor cells and activated host B cells.

We have examined the cellular changes taking place in rat popliteal lymph nodes undergoing a graft-versus-host (GvH) reaction. Examination of immunoperoxidase-stained lymph node sections, using a panel of mouse monoclonal antibodies directed against different rat lymphoid cell subsets, revealed a disorganization of the lymph node architecture with disappearance of the follicles, and an intermingling of T and B cells, so that no distinct T- and B-cell areas were visible any more. Since the GvH nodes showed a preferential accumulation of host B cells over host T cells (particularly over the W 3/25+ T helper cell subset), we also investigated the requirements for host B cell activation. The popliteal lymph node GvH reaction was induced in (PVG X DA)F1 rats by the injection of PVG cells into one foot and by DA cells into the other foot, and then immunoglobulin kappa allotype marked PVG B cells from athymic donors were injected intravenously. The allotype marked B cells proliferated vigorously in response to the DA T cells, but much less in response to the PVG T cells. These results indicate that the massive B-cell activation taking place in GvH reactions may require an alloantigen incompatibility between donor T cells and host B cells, and argue against non-specific mitogenic induction of the B cells.

The effects of cyclosporin on lymphocyte activation in a systemic graft-vs.-host reaction.

We have investigated the effects of cyclosporin (CsA) on each of three stages of lymphocyte activation in vivo viz. sequestration of alloantigen-reactive lymphocytes from the circulation into the spleen and lymph nodes, blast transformation and induction of DNA synthesis in the activated cells and release of these cells and their progeny into the circulation. Parental strain lymphocytes injected i.v. into semi-allogeneic rats and recovered from the thoracic duct within 36 h are profoundly unresponsive in a local graft-vs.-host assay to the alloantigens of the F1 hybrid but have normal activity against unrelated alloantigens (negative selection). CsA treatment of the F1 hybrid recipients did not prevent this selective sequestration of antigen-reactive cells. In the untreated F1 hybrid, from 36 h after injection, large numbers of dividing blast cells were released into the lymph. These cells did not appear in the lymph of recipients treated with CsA. However, CsA did not prevent the activation of cells sequestered in the spleen or lymph nodes as assessed by [3H] thymidine incorporation and autoradiography. This unexpected finding suggests that CsA inhibits lymphocyte responses to alloantigens in vivo after DNA synthesis which is a later stage than the in vitro studies have shown.

Functional and morphological changes in post-capillary venules in relation to lymphocytic infiltration into BCG-induced granulomata in rat skin.

Vessels identical to lymph node high endothelial venules (HEV) have been described in sites of non-lymphoid tissue lymphocyte accumulation. In this study the function of these (HEV-like) vessels has been investigated in BCG-induced skin lesions in the rat. By following the traffic of radiolabelled lymphocytes from the blood into the lesions the HEV-like vessels have been shown to be the preferred site of migration. The complicated development of the vessels has been studied and an hypothesis advanced to explain their inter-relationship with tissue and circulating lymphocytes.

The organization of cell populations within lymph nodes: their origin, life history and functional relationships.

The normal lymph node comprises a superficial cortex, a deep cortex or paracortex and a medulla. In each of these regions there are three kinds of spaces: an intralymphatic space, an intravascular space and an extravascular space or interstitium. Both the vascular endothelium and the lymphatic endothelium are specialized in these different regions. The cell types in lymph nodes comprise lymphoid cells, accessory or non-lymphoid cells and stromal cells, and within these cell types a number of different sub-types can now be identified by means of enzyme- and immunocytochemistry. Based predominantly on experimental studies, the origin, migratory patterns, localization, inter-relationships and interactions between these various cells are reviewed.

The carriage and delivery of substances to lymphatic tissues by recirculating lymphocytes. I. The concentration of ricin in lymphocyte traffic areas.

Thoracic duct lymphocytes (TDL) were loaded in vitro with ricin before intravenous injection into syngeneic rats. TDL that had been incubated at 10 micrograms of ricin/5 X 10(7) cells/ml migrated from the blood into the spleen and lymph nodes (LN) according to the physiological pattern, and TDL incubated at 10 times that concentration were only slightly impaired in their ability to enter LN. The transfer of cells to recipients with thoracic duct fistulae indicated that very few ricin-treated lymphocytes left the LN to recirculate back to lymph. Most of the ricin-loaded lymphocytes died within the lymphatic tissues, probably between 7 and 15 hr after injection. The ricin toxicity was transferred locally, causing selective damage to the cell population within the traffic areas of the lymphatic tissues without disrupting the tissue architecture. This pattern of intensive cell destruction was not seen after a lethal dose of free ricin, which caused more diffuse and less severe damage to the spleen and LN, proving that lymphocytes are effective carriers of ricin. The surviving host lymphocytes were distributed abnormally, presumably because of the obvious damage to small blood vessels in LN and elsewhere. Lymphocytes accumulated especially in the red pulp of the spleen. Although the method described has drawbacks, it might be developed in order to concentrate ricin in the vicinity of neoplastic cells in diffuse lymphomas and leukaemias.

The rapid rejection of allogeneic lymphocytes by a non-adaptive, cell-mediated mechanism (NK activity).

The fate of allogeneic lymphocytes (AO or DA) transferred to non-immune PVG recipients was studied in the light of previous evidence (Heslop & McNeilage, 1983; Rolstad & Ford, 1983) that allogeneic lymphocytes can be rapidly destroyed in certain strain combinations of rats and mice by a mechanism that is distinct from either T-cell mediated immunity or an alloantibody response. AO lymphocytes injected into PVG recipients were discriminated from syngeneic lymphocytes within 15-30 min of i.v. injection, as testified by the excess release of 51Cr into the lymph plasma of the recipient. The following experiments were intended to distinguish between natural antibody and natural killer (NK) cells as the mechanism responsible for the allogeneic lymphocyte cytotoxicity (ALC) displayed by PVG rats. Nude rats treated from birth with anti-mu chain serum and shown to be lacking B and T lymphocytes, as well as being profoundly deficient in immunoglobulin, displayed more aggressive ALC than did control nude rats which, in turn, showed stronger ALC than did euthymic rats. Serum from PVG nude rats exerted no inhibitory or destructive effect on allogeneic lymphocytes in an antibody-dependent cellular cytotoxicity system, an assay of graft-versus-host activity, or when injected into 3-4-week-old PVG rats which had not yet developed ALC. Treatment of nude rats with anti-asialo GM 1 antiserum depressed ALC and NK activity in parallel, thus adding to a wide range of circumstances in which ALC and NK activity are closely correlated. In conclusion, ALC is implemented by a non-adaptive, cell-mediated mechanism independent of immunoglobulin, but the precise identity of the effector cell in the recipients' lymphatic tissues remains to be settled.