Conscious agency vs. pre-conscious sensory filtering: Disparate suppression of trigeminal blink reflex by self-stimulation and by prepulses

Modulation of the blink reflex (BR) to supraorbital nerve (SON) stimulation by a weak somatosensory prepulse (sPP) consists of inhibition of R2 and facilitation of R1. Similar BR changes occur with self-stimulation. Our aim was to compare neurophysiological processes underlying both effects. We assessed BR parameters in 18 healthy participants following right SON stimulation either performed by an experimenter (experiment 1A) or following self-stimulation (experiments 1B, 1C). In experiments 1A and 1C, sPPs to digit 2 preceded SON stimuli by 40, 100, 200 and 500 ms. In experiment 1B: self-stimulation was delayed by 40, 100, 200, and 500 ms. In experiment 2, BRs were elicited by an experimenter randomly during a 2-s period before participants applied self-stimulation. In experiment 1, as expected, sPPs caused facilitation of R1 and inhibition of R2, which peaked at 100 ms ISI, similarly in experiments 1A and 1C. Self-stimulation caused a decrease of R2, which was evident in a broad range of time intervals. In experiment 2, R2 was already inhibited at the onset of the 2-s period, while R1 began to rise significantly 1.4 s before self-stimulation. Both effects progressively increased until self-triggering. The results concur with a time-locked gating mechanism of prepulses at brainstem level, whereas self-stimulation modulates BR in a tonic manner, reflecting a cognitive influence due to self-agency.

Prepulse inhibition vs cognitive modulation of the hand-blink reflex

The excitability of brainstem circuitries mediating defensive blinking in response to abrupt sensory inputs is continuously modulated by cortical areas, e.g., the hand-blink reflex (HBR), elicited by intense electrical median nerve stimulation, is enhanced when the stimulated hand is close to the face, with the behavioural purpose to optimize self-protection from increased threat. Here we investigated whether such cortically mediated HBR facilitation can be influenced by prepulse inhibition (PPI), which is known to occur entirely at the subcortical level. Twenty healthy volunteers underwent HBR recordings in five experimental conditions. In conditions 1 and 2, the stimulated hand was held either near (1) or far (2) from the face, respectively. In conditions 3 and 4, stimulation of the hand near the face was preceded by a peri-liminal prepulse to the index finger of the contralateral hand held either near (3) or far from the face (4). In condition 5, participants self-triggered the stimulus eliciting the HBR. We observed a reproducible HBR in 14 out of 20 participants and measured onset latency and area of the HBR in orbicularis oculi muscles bilaterally. HBR area decreased and latency increased in condition 2 relative to condition 1; HBR area decreased and latency increased markedly in condition 3, and somewhat less in condition 4, relative to conditions 1 and 2; self-stimulation (condition 5) also suppressed HBRs, but less than prepulses. These findings indicate that PPI of the HBR is more robust than the cognitive modulation exerted by top-down cortical projections. Possibly, an attentional shift to a prepulse may serve to reduce blinking in response to perturbation when it is convenient, in a given situation, not to interrupt ongoing visual processing.

When reflex reactions oppose voluntary commands: The StartReact effect on eye opening

A startling auditory stimulus (SAS) induces a reflex response involving, among other reactions, a strong contraction of the orbicularis oculi muscle (OOc) and subsequent eye closure. A SAS also induces the StartReact effect, a significant shortening of reaction time in subjects ready for task execution. We examined the obvious conflict appearing when a StartReact paradigm requires participants with eyes closed to open their eyes to look for a visual target. We recorded OOc EMG activity and eyelid movements in healthy volunteers who were instructed to open their eyes at perception of a somatosensory imperative stimulus (IS) and locate the position of a Libet's clock's hand shown on a computer screen at 80 cm distance. In 6 out of 20 trials, we delivered a SAS simultaneously with the IS. The main outcome measures were reaction time at onset of eyelid movement and the time gap (TG) separating subjective assessment of the clock's hand position from real IS issuing. Control experiments included reaction time to eye closing and target location with eyes open to the same IS. Reaction time was significantly faster in SAS than in noSAS trials and slower for eye opening than for eye closing in both conditions. In the eye-opening task, TG was significantly shorter in SAS with respect to noSAS trials, despite the presence of the SAS-related burst in the OOc before EMG cessation. Our results indicate that the StartReact effect speeds up eye opening and location of a target in the visual field despite the startle reaction opposing the task.

Understanding hyper-reflexia in acute motor axonal neuropathy (AMAN)

Hyper-reflexia is occasionally seen in acute motor axonal neuropathy (AMAN), but its pathophysiology is unclear. We report a patient with AMAN following Campylobacter jejuni enteritis, who showed generalized hyper-reflexia, bilateral Hoffmann sign and right Babinski sign. MRI and transcranial magnetic stimulation of the motor cortex disclosed no corticospinal tract involvement. An extensive electrophysiological investigation documented α-motoneuron hyperexcitability and dysfunction of the interneuronal inhibitory circuits in the spinal anterior horn. We propose an immune-mediated damage of the spinal inhibitory interneuronal network as possible mechanism inducing hyper-reflexia in AMAN.

Threat vs control: Potentiation of the trigeminal blink reflex by threat proximity is overruled by self-stimulation

The magnitude of the defensive blink reflex is modulated by continuous assessment of its protective value. Here, we studied whether the trigeminal blink reflex (TBR) is modulated by a potentially offensive object close to the face, and, if so, whether self-stimulation or observation of the act of stimulus triggering counteracts such modulation. In all, 26 healthy volunteers participated in various experimental conditions. At baseline, an experimenter triggered supraorbital nerve stimuli remotely, unseen by the participants; in experimental conditions, the experimenter held a stimulation probe close to the participant's face but triggered the stimuli either remotely, "surprising" participants (S₁ ), or directly on the probe, observed by participants (S₂ ). In other conditions, participants triggered stimuli themselves on the probe held next to their body (S₃ ) or held in front of their face (S₄ ). The latter condition was repeated similarly, but pressing the button only randomly generated electrical stimuli (S5, "Russian roulette"). The size of the R2 component of the TBR (TBR-R2) was the main outcome measure. Compared to baseline, TBR-R2 area was significantly larger in S₁ when the "threatening" probe was close to the face and the participant had no control over stimulation. Conversely, TBR-R2 was suppressed when participants either saw the action of triggering, thus being aware (S₂ ), or had full initiative over stimulation (S₃ , S₄ ). Random self-generated stimuli (S₅ ) inhibited TBR-R2, but to a lesser extent than S₃ and S_4. Perceived threat close to the face facilitates TBR-R2, but knowledge about impending stimulation or self-agency overrules this effect.

Influence of posture on blink reflex prepulse inhibition induced by somatosensory inputs from upper and lower limbs

BACKGROUND

Prepulse inhibition (PPI) is a neurophysiological phenomenon whereby a weak stimulus modulates the reflex response to a subsequent strong stimulus. Its physiological purpose is to avoid interruption of sensory processing by subsequent disturbing stimuli at the subcortical level, thereby preventing undesired motor reactions. An important hub in the PPI circuit is the pedunculopontine nucleus, which is also involved in the control of posture and sleep/wakefulness.

OBJECTIVE

To study the effect of posture (supine versus standing) on PPI, induced by somatosensory prepulses to either upper or lower limb. PPI was measured as the percentage inhibition of the blink reflex response to electrical supraorbital nerve (SON) stimulation.

METHODS

Sixteen healthy volunteers underwent bilateral blink reflex recordings following SON stimulation either alone (baseline) or preceded by an electrical prepulse to the median nerve (MN) or sural nerve (SN), both in supine and standing. Stimulus intensity was 8 times sensory threshold for SON, and 2 times sensory threshold for MN and SN, respectively. Eight stimuli were applied in each condition.

RESULTS

Baseline blink reflex parameters did not differ significantly between the two postures. Prepulse stimulation to MN and SN caused significant inhibition of R2. In supine but not in standing, R2 was significantly more inhibited by MN than by SN prepulses. In standing, SN stimulation caused significantly more inhibition of R2 than in supine, while the inhibition caused by MN prepulses did not differ significantly between postures.

SIGNIFICANCE

PPI induced by lower limb afferent input may contribute to postural control while standing.

Adult-Onset Gilles de la Tourette Syndrome: Psychogenic or Organic? The Challenge of Abnormal Neurophysiological Findings

Gilles de la Tourette syndrome (GTS) is characterized by multiple motor and vocal tics. Adult-onset cases are rare and may be due to "reactivation" of childhood tics, or secondary to psychiatric or genetic diseases, or due to central nervous system lesions of different etiologies. Late-onset psychogenic motor/vocal tics resembling GTS have been described. Neurophysiology may serve to differentiate organic from functional GTS. Altered blink reflex pre-pulse inhibition (BR-PPI), blink reflex excitability recovery (BR-ERC), and short-interval intracortical inhibition (SICI) have been described in GTS. We report a 48-years-old male, who developed numerous motor/vocal tics 2 months after sustaining non-commotional craniofacial trauma in a car accident. Both his father and brother had died earlier in car crashes. He presented with blepharospasm-like forced lid closure, forceful lip pursing, noisy suction movements, and deep moaning sounds, occurring in variable combinations, without warning symptoms or internal "urge." Tics showed low distractibility and these increased with attention. Standard magnetic resonance imaging, electroencephalography, and evoked potentials were unremarkable. Neuropsychology diagnosed moderately impaired intellect, attention, and executive functions. Psychiatric assessment revealed somatization disorder and generalized anxiety. BR-PPI was unremarkable, while BR-ERC was enhanced, even showing facilitation at short intervals. SICI was markedly reduced at 1 and 3 ms and intracortical facilitation (ICF) was enhanced at 10 ms. The patient fulfilled Fahn and Williams' diagnostic criteria for a psychogenic movement disorder. Neurophysiology, however, documented hyperexcitability of motor cortex and brainstem. We suggest that-similar to what has been reported in psychogenic dystonia-a pre-existing predisposition may have led to the functional hyperkinetic disorder in response to severe psychic stress.

Modulation of exteroceptive electromyographic responses in defensive peripersonal space

The cutaneous silent period (CSP) to noxious finger stimulation constitutes a robust spinal inhibitory reflex that protects the hand from injury. In certain conditions, spinal inhibition is interrupted by a brief burst-like electromyographic activity, dividing the CSP into two inhibitory phases (I1 and I2). This excitatory component is termed long-loop reflex (LLR) and is presumed to be transcortical in origin. Efficient defense from environmental threats requires sensorimotor integration between multimodal sensory afferents and planning of defensive movements. In the defensive peripersonal space (DPPS) immediately surrounding the body, we interact with objects and persons with increased alertness. We investigated whether CSP differs when the stimulated hand is in the DPPS of the face compared with a distant position. Furthermore, we investigated the possible role of vision in CSP modulation. Fifteen healthy volunteers underwent CSP testing with the handheld either within 5 cm from the nose (near) or away from the body (far). Recordings were obtained from first dorsal interosseous muscle following index (D2) or little finger (D5) stimulation with varying intensities. A subgroup of subjects underwent CSP recordings in near and far conditions, both with eyes open and with eyes closed. No inhibitory CSP parameter differed between stimulation in near and far conditions. LLRs occurring following D2 stimulation were significantly larger in near than far conditions at all stimulus intensities, irrespective of subjects seeing their hand. Similar to the hand-blink reflex, spinally organized protective reflexes may be modulated by corticospinal facilitatory input when the hand enters the DPPS of the face. NEW & NOTEWORTHY The present findings demonstrate for the first time that a spinally organized protective reflex, the cutaneous silent period (CSP), may be modulated by top-down corticospinal facilitatory input when the stimulated hand enters the defensive peripersonal space (DPPS) of the face. In particular, the cortically mediated excitatory long-loop reflex, which may interrupt the CSP, is facilitated when the stimulated hand is in the DPPS, irrespective of visual control over the hand. No spinal inhibitory CSP parameter differs significantly in or outside the DPPS.

Atypical Electrophysiological Findings in a Patient with Acute Motor and Sensory Axonal Neuropathy

Guillain–Barré syndrome (GBS) is an immune-mediated polyradiculoneuropathy with acute onset and rapid clinical worsening; early diagnosis and immunomodulating therapy can ameliorate the course of disease. During the first days, however, nerve conduction studies (NCSs) are not always conclusive. Here, we describe a 73-year-old man presenting with progressive muscular weakness of the lower limbs, ascending to the upper limbs, accompanied by distal sensory disturbances. Neuroimaging of brain and spine and NCSs were unremarkable; cerebrospinal fluid analysis revealed no albuminocytologic dissociation. Based on typical clinical features, and on positivity for serum GD1b-IgM antibodies, GBS with proximal conduction failure at multiple radicular levels was postulated, and a standard regime of intravenous immunoglobulin was administered. Four weeks later, the patient presented with flaccid tetraparesis, areflexia, and reduction of position sense, tingling paresthesias, and initial respiratory distress. Repeat NCS still revealed almost normal findings, except for the disappearance of right ulnar nerve F-waves. A few days thereafter, the patient developed severe respiratory insufficiency requiring mechanical ventilation for 2 weeks. On day 50, NCS revealed for the first time markedly reduced compound muscle action potentials and sensory nerve action potentials in all tested nerves, without signs of demyelination; needle electromyography documented widespread denervation. The diagnosis of acute motor and sensory axonal neuropathy was made. After 3 months of intensive rehabilitation, the patient regained the ability to walk with little assistance and was discharged home. In conclusion, normal NCS findings up to several weeks do not exclude the diagnosis of GBS. Very proximal axonal conduction failure with late distal axonal degeneration should be taken into consideration, and electrodiagnostic follow-up examinations, even employing unusual techniques, are recommended over several weeks after disease onset.

Alendronate Reduces Bone Resorption in HIV-Associated Osteopenia/Osteoporosis

PURPOSE

To evaluate the effects of alendronate, vitamin D, and calcium supplementation on bone metabolism and bone mineral density (BMD) in both HIV-infected men and women treated with highly active antiretroviral therapy (HAART).

METHOD

We performed a 52-week prospective, multicenter, randomized, open-label clinical trial. Eligible participants were on stable HAART and had BMD values at the femoral neck or lumbar spine that corresponded to a t score less than -1. Patients were randomized to receive alendronate 70 mg weekly or no alendronate; calcium 1000 mg daily and vitamin D 500 IU daily were provided to all study recipients. Primary endpoint of the study was the change in bone metabolism evaluated by N-telopeptide of type 1 collagen and bone-specific alkaline phosphatase; the secondary endpoint was BMD variation.

RESULTS

18 patients were randomized to the alendronate and 23 to the no-alendronate group (controls). The alendronate-treatment group compared to controls had a significant decrease in serum N-telopeptides, 1914 +/- 1433.4 vs. 3967 +/- 1650.5 pM/L (p = .005) after 1 year. Lumbar spine BMD increased by 4% in the alendronate group (p = .004) vs. 3.7% (p = .062) in controls, compared to baseline values. Femoral neck BMD decreased by 0.5% in the alendronate group (p = .05) and by 3.5% in the control group (p = .04). No between-groups differences for BMD were found (Delta lumbar-BMD 0.0351 +/- 0.0406 in cases and 0.0356 +/- 0.073 in controls [p = .977], Delta femoral-BMD -0.085 +/- 0.160 in cases and -0.100 +/- 0.165 in controls [p = .795]).

CONCLUSION

Alendronate plus vitamin D and calcium was effective in reducing bone resorption. Alendronate improved lumbar BMD and minimized femoral BMD decrease after 52 weeks compared to treatment with vitamin D and calcium alone in patients on HAART with osteopenia/osteoporosis.

Coherence and Consciousness: Study of Fronto-Parietal Gamma Synchrony in Patients with Disorders of Consciousness

Evaluation of consciousness needs to be supported by the evidence of brain activation during external stimulation in patients with unresponsive wakefulness syndrome (UWS). Assessment of patients should include techniques that do not depend on overt motor responses and allow an objective investigation of the spontaneous patterns of brain activity. In particular, electroencephalography (EEG) coherence allows to easily measure functional relationships between pairs of neocortical regions and seems to be closely correlated with cognitive or behavioral measures. Here, we show the contribution of higher order associative cortices of patients with disorder of consciousness (N = 26) in response to simple sensory stimuli, such as visual, auditory and noxious stimulation. In all stimulus modalities an increase of short-range parietal and long-range fronto-parietal coherences in gamma frequencies were seen in the controls and minimally conscious patients. By contrast, UWS patients showed no significant modifications in the EEG patterns after stimulation. Our results suggest that UWS patients can not activate associative cortical networks, suggesting a lack of information integration. In fact, fronto-parietal circuits result to be connectively disrupted, conversely to patients that exhibit some form of consciousness. In the light of this, EEG coherence can be considered a powerful tool to quantify the involvement of cognitive processing giving information about the integrity of fronto-parietal network. This measure can represent a new neurophysiological marker of unconsciousness and help in determining an accurate diagnosis and rehabilitative intervention in each patient.

Socio-economic differences in healthcare access from a welfare system perspective, Italy: 2007-2010

Inequalities between poorer and wealthier people in accessing healthcare services have been widely studied, but the mechanisms generating them are still to be fully understood. Among these, there is still a lack of evidence of relationships between health prevention/health promotion policies, welfare systems and social differences. We analysed 68 201 females from the PASSI Italian surveillance system for the years 2007-2010. The prevalence of women undergoing Pap testing was used as an example of access to preventive services. An odds ratio gradient was found with regard to different welfare system clusters: the probability of undergoing a screening test is higher for more advanced welfare systems. A strong association was found between having received a letter from the local health unit and having undergone the screening test. Significant differences still exist between high- and low-income women and their access to Italian preventive public services. As we expected, social determinants play an important role in health disparities, as these are also strongly influenced by typologies of welfare systems and by health policies.

Enhancing global capacity in the surveillance, prevention, and control of chronic diseases: seven themes to consider and build upon

BACKGROUND

Chronic diseases are now a major health problem in developing countries as well as in the developed world. Although chronic diseases cannot be communicated from person to person, their risk factors (for example, smoking, inactivity, dietary habits) are readily transferred around the world. With increasing human progress and technological advance, the pandemic of chronic diseases will become an even bigger threat to global health.

METHODS

Based on our experiences and publications as well as review of the literature, we contribute ideas and working examples that might help enhance global capacity in the surveillance of chronic diseases and their prevention and control. Innovative ideas and solutions were actively sought.

RESULTS

Ideas and working examples to help enhance global capacity were grouped under seven themes, concisely summarised by the acronym "SCIENCE": Strategy, Collaboration, Information, Education, Novelty, Communication and Evaluation.

CONCLUSION

Building a basis for action using the seven themes articulated, especially by incorporating innovative ideas, we presented here, can help enhance global capacity in chronic disease surveillance, prevention and control. Informed initiatives can help achieve the new World Health Organization global goal of reducing chronic disease death rates by 2% annually, generate new ideas for effective interventions and ultimately bring global chronic diseases under greater control.

Assessment of adequacy of ICU admission

BACKGROUND

Direct costs of critical care are increasing more than in other health care sectors. Tools are needed to evaluate adequacy of ICU admission in order to have a proper allocation of ICU resources.

OBJECTIVE

evaluation of different ways used to assess adequacy of ICU admission.

METHODS

STUDY TYPE

12 months prospective descriptive study.

SETTING

24 Intensive Care beds of a 1000 beds tertiary hospital in Italy.

PATIENTS

2314 patients admitted to Cardiac Surgery, General and Postoperative Intensive Care Units.

INTERVENTIONS

all patients admitted to the ICUs were studied. Information was collected for the patients' age, source of admission, diagnoses, surgical status, reason for admission, SAPS II score, NEMS daily score, LOS, ICU outcome. The number of available beds (ventilated or not) and nurse working hours were obtained.

RESULTS

2373 patients were admitted to the ICs, with an overall readmission rate of 2.5%, and a total amount of 8084 NEMS record. The mean Work Utilization Ratio was significantly different between the three IC and between working and weekend days in PACU and CSU. The 49.7% of the NEMS points is scored by the SAPS II 43-78 patients, corresponding to the 29.2% of >24 h admissions. The level of care provided and the trend of each admission was derived from NEMS score according to Iapichino. The proportion of HT records in each IC was 88.3% in ICU, 73.1% in PACU and 91.2% in CSU; the outcome (dead/discharged) was significantly different between LT and HT.

CONCLUSIONS

Despite the difficulties imposed by he rigid nurses' work organization in Italy, a daily data collection about level of care, severity of illness, workload utilization could provide, together with standard administrative indexes, the necessary framework to assess and to improve adequacy of ICU admission.

Subgroup-specific effects of questionnaire wording on population-based estimates of mammography prevalence

OBJECTIVES

This study investigated whether an apparent downturn in prevalence rates of mammography use reported in the 1992 Behavioral Risk Factor Surveillance System (BRFSS) questionnaire resulted from a change in questionnaire wording.

METHODS

In a pretest-posttest design (1990-1991 vs 1992), piecewise linear regression analyses were based on monthly prevalence estimates of mammography use among female BRFSS respondents 40 years or older.

RESULTS

Self-reported mammography use was lower by 3.5 percentage points (95% confidence interval [CI] = 1.5, 5.5) overall--and lower by 13.6 percentage points (95% CI = 2.6, 24.6) among Black women with less than a high school education--when predicted from 1992 data than when predicted from 1990-1991 data.

CONCLUSIONS

A change in questionnaire wording in the BRFSS caused demographic-specific effects in population-based estimates of mammography use.

The influence of socioeconomic status on health service utilisation by patients with AIDS in north Italy. The North-East Italian Group for Planning of AIDS Health Care

Evidence for an association between socioeconomic status (SES) and health service utilisation (HSU) by patients with AIDS is examined using data for an Italian AIDS study population. A composite measure of SES which takes into account several key variables was developed using Multiple Correspondence Analysis. A classification of SES categories (high, medium-high, medium-low, low) was constructed and resource utilisation across the categories compared. The study population were patients with AIDS referred to 10 AIDS clinics in the study area in North-East Italy. A questionnaire survey was undertaken over the period January to June 1994, and was completed by 555 patients. Statistical analysis was conducted, using log-linear modelling, of health service utilisation (covering inpatient and day care) by SES categories, illness severity and HIV transmission route group. The analysis demonstrated that SES has a statistically significant association with variation in HSU, secondary in importance to severity of illness. This finding has important implications for future care planning for HIV/ AIDS in Italy, and potentially to other countries. Further research is needed to examine the relationship between SES and health service utilisation and costs in Italy and in other European countries.

Efficiency and rationality in the planning of health care for people with AIDS: an application of the balance of care approach. North-East Italian Group for Planning of AIDS Health Care

OBJECTIVE

To demonstrate the application of an approach for assessing efficiency and rationality in the use of resources for the care of patients with AIDS (PWA), using data for north-east Italy.

DESIGN

An economic methodology, the balance of care (BoC) approach, enabled identification of scenarios for the current, planned and recommended provision of care in the study region.

METHODS

Data on the supply and utilization of care by PWA across four locations (inpatient care, day care, home care and sheltered accommodation) was collected for a 6-month period during 1994. The current BoC measured in care contacts across the locations was compared with a planned BoC scenario, derived from the Italian AIDS Health Plan, and a recommended BoC scenario based on a delphi expert panel judgement of the appropriate care location according to sets of hypothetical clinical and social characteristics of PWA. The cost consequences of reallocating patient contacts between the current BoC to the recommended BoC was assessed for inpatient and day care contacts.

RESULTS

There is an overprovision of home care in the planned BoC scenario if applied to the study region. The cost consequences of a shift of care contacts according to the recommended scenario results in a potential cost reduction of 9.2% compared with the current scenario, and hence an expected efficiency improvement.

CONCLUSION

The BoC approach can be applied to improve the efficiency and rationality of resource use in planning care provision for PWA.

[Indirect morbidity indicators and social differences in the ISTAT quarterly workforce survey]

Information on the health condition job related of the population are often collected in specific studies, usually limited over time and concerned with a small part of the general population. Looking at official statistics, sources such as national health surveys (in Europe and in North America) are rich on health data, but often offer little information on job-conditions, and job history. On the other hand, one also can find official sources, mainly concerned with labour and job related topics, in which information related to the health status of the people interviewed are routinely collected. These are the Labour Force Surveys, carried out in the most of developed countries. In the Italian Labour Force Survey (RTFL) the Italian Statistical Institute (ISTAT) quarterly collects information on health-related sick absence, part-time job and unemployment. Data from RTFL of two Italian regions (Lombardy: 1985, '86, '89 and Veneto: 1985, '86) show differentials by age and job-position that are consistent with expectation, encouraging an extensive use of this source for surveillance purposes at the national and regional level.

[An index of HIV infection risk in the population]

The paper presents a risk index constructed on the basis of some sexual behaviour-related variables. It is intended for measuring the risk of exposure to HIV infection for the general population. Variables are from a study on Lifestyle and Health conducted on a sample of the population living in the London, Edinburgh, and Glasgow metropolitan area by the Research Unit in Health and Behavioural Change at the Edinburgh University. The construction of the index has been realized through a delphi study which has collected information from a panel of AIDS national experts. Methodological problems in summarising information coming from several variables are discussed. The main task of the study is not to provide a total prediction of HIV infection in the population of Britain, but to assess the component which may stem from sexual behaviours when estimated from self-reports. Major findings are the consistency of the population in the "medium risk" group, that, if a spread of AIDS among the heterosexual population can be hypothesized, gives a rather pessimist scenario. Moreover, a trend analysis (possible because of the continuity in the data collection) shows an increase in this "medium risk" group, although the "high risk" group appears much less consistent (less than two percent) and slowly declining over time.

Sexual behavior and exposure to HIV infection: estimates from a general-population risk index

OBJECTIVES

The spread of the human immunodeficiency virus (HIV) in the general population has been a much debated topic in the mass media. The aim of this study was to create an approach to estimating the risk of exposure to HIV resulting from sexual behaviors.

METHODS

A theoretical estimate was applied to data obtained from a large-scale risk factor survey carried out in Britain. An HIV infection-exposure risk index was constructed by ranking different sex-related categorizations derived from variables in the survey.

RESULTS

The risk index involved a Delphi-based assessment of self-reported behavioral factors associated with HIV exposure and subsequent transmission. Roughly 85% of the adult population aged 18 to 50 were estimated to be at some risk for behavioral exposure to HIV virus with regard to reported sexual behavior. Over time, those who could be considered at no risk have declined as a proportion of the population.

CONCLUSIONS

The estimates appear to refute commonplace assertions that exposure to HIV through sexual behavior is not a problem for general populations.