Challenges Faced by Individuals with Hearing Impairment during COVID-19 Pandemic Lockdown in India - A Pilot Study

COVID - 19 (Corona Virus Infectious Disease) situations reported in 2019, declared by World Health Organization (WHO) as a pandemic is still a prevailing global crisis. Common regulations were implemented such as lockdown, wearing face masks as mandatory, face shields, gloves and maintaining physical and social distance in public places to reduce the spread of the virus. These pandemic induced challenges affected social communication, technical and behavioral aspects in lifestyle of people with hearing impairment. Along with medical, paramedical services, the crisis had challenged hearing, speech language pathology and therapy services too. The study aimed to explore the challenges that adults with hearing impairment had experienced during the pandemic and to suggest some practical solutions that can be implemented by audiologists. It is a questionnaire-based study with purposive sampling method employed in data collection. The questionnaire was administered on adult hearing aid users (mean age: 18 years) recruited for participation from different parts/ clinical setups across India. The outcome of the questionnaire did support the assumption that availing audiological services was difficult or impossible for most of the hearing aid users. Accessing batteries was reported to be the most frequent issue. Adequate level of hearing though hearing aid was important to them and clinical services could not be availed for long period of time due to travel related issues and closure of audiological services. Also, social isolation impacted on their quality of life and effective communication. As a possible solution most of the users chose tele services as a better solution.

Education Intervention on 'Hearing Impairment - Its Assessment and Management' among Medical Practitioners in Sikkim, India

BACKGROUND

Health care providers must be aware of the choices in aural rehabilitation methods and assessment procedures available presently to those with hearing impairment in order to facilitate early identification and intervention and ensure quality of care to those hearing impaired individuals. The referrals from the medical fraternities for the audiological services are not uniform across India. Part of reason may be that awareness about the roles of and responsibilities of audiologist's is poor among medical practitioners. In some regions of India medical practitioners may be only grossly be aware of audiologists per se. They may not know enough to refer all individuals with hearing or balance disorders for the required audiological services.

AIM

To evaluate changes in pre survey and post survey after education intervention specifically planned for medical practitioners in the state of Sikkim, India. Education intervention included awareness about hearing impairment and its assessment and management by audiologists.

METHOD

A pre and post survey comparison research design with purposive convenient sampling technique was applied. Participants were medical practitioners working in geographical area of Sikkim at the time of the study. Inspection of demographic data of respondents showed that they were in their age range of 24 and 60 years and with work experience ranging 1-40 years. Participants were invited for an awareness talk which included, information about hearing loss, early identification and early intervention, tests and management of hearing loss in different age groups, need for hearing aids/cochlear implants, auditory training, and the role of an audiologist in the management of hearing loss and ways to prevent hearing loss. A pre and post awareness program responses were collected from all the participants using a customized questionnaire tool.

RESULTS

Respondents exhibited, in the pre-survey questionnaire, lack of awareness in many aspects of audiology, including assessing hearing impairment, diagnosing hearing loss, and the role of an audiologist. There was an overall, statistically significant difference in the level of performance on the pre-awareness and post-awareness responses.

CONCLUSION

Following an awareness campaign among the medical professionals in Sikkim, there was a considerable change in their level of awareness of hearing impairment, its assessment, and management by audiologists. The reach of the awareness campaign was significant as around 70% of subjects showed significant change in their knowledge and attitude towards hearing impairment, its management.

Adaptation of Morningness-Eveningness Questionnaire (MEQ) in Bengali Language

BACKGROUND

Morningness-Eveningness Questionnaire (MEQ) has been used to assess working efficiency of an individual. The self-reporting MEQ is available in English language, and its applicability to Indian scenario is limited to educated/ English proficient individuals only. Since, majority in India still depend on the regional languages for communication, it is difficult to make live translation of the questionnaire while administration and results may also vary due to tester's language proficiency. The present study focused on adapting MEQ in Bengali language.

METHOD

The English version of Morningness-Eveningness Questionnaire (MEQ) was a self-assessment questionnaire consisting of 19 questions to measure whether a person's peak alertness was in the morning, evening or in between. The translation of the questionnaire was done using forward-backward-translation method by six experts in Bengali language, and was content validated by thirty native Bengali speakers. The speakers were asked to rate the questions on a 5-point rating scale with 1 being very familiar and 5 being not at all familiar. All the questions rated as 1 or 2 were considered for the Bengali version of MEQ, while those rated as 3 or above were reframed and revalidated.

RESULT

The Bengali version of the MEQ has good reliability (Cronbach's alpha 0.74). Item analysis revealed it as a good consistent scale for estimating the circadian type of the participants. Participants were classified into 5 Circadian types based on the cut-off scores. Majority of participants are intermediate type, followed by Morningness.

CONCLUSION

The application of MEQ will help in management of tinnitus.

Dentists Role in Psychological Screening and Management of Head-and-neck Cancer Patients Undergoing Radiotherapy - Narrative Review

Objectives

Head-and-neck cancer management primarily involves surgery and chemoradiotherapy. Recurrent radiotherapy (RT) sessions are often linked to social, physical, and psychological burdens. Oral physicians are part of the palliative care team and play a pivotal role in decimating the physical side effects associated with disease and its treatment. There is a need to familiarise dentists with the psychological aspect of the treatment.

Material and Methods

Various libraries were searched from the year 2012 to 2022. A total of nine studies that had head-and-neck RT patients exclusively were included in the study.

Results

Anxiety and depression are patients' most prevalent psychological problems during and after the RT regimen. A few most used psychological screening tools were identified.

Conclusion

Dental professionals are uneducated about the holistic approach to managing RT patients. The current narrative review details the various psychological screening tools and care measures that can be incorporated into the dental setup to help these patients.

Diethylcarbamazine citrate-fortified salt for lymphatic filariasis elimination in India

Lymphatic filariasis (LF) is a vector-borne neglected tropical disease, causing permanent disability. The disease is debilitating and widespread, leading to tremendous productivity and economic loss. The Government of India (GOI) prioritized the elimination of LF through the annual mass drug administration (MDA) programme in 2004 and continued with a single dose of diethylcarbamazine citrate (DEC), 6 mg/kg of body weight, plus albendazole annually over a period of 5-6 years. The GOI had set the target to achieve LF elimination by 2015 and now by 2030. The progress so far has been suboptimal. Much remains to be done as about 84 per cent of the total 328 endemic districts are still under MDA. The major challenge in implementing MDA is poor compliance. It is necessary to have a feasible alternative strategy addressing the above challenge to achieve the desired goal of LF elimination. At this juncture, a well-researched approach, i.e. the use of DEC-fortified salt, also advocated by the World Health Organization, as a unique form of MDA, is proposed. As per this strategy, a low dose of DEC (0.2% w/w) is added to the cooking salt at the manufacturing facility of iodized salt and consumed by the LF-endemic communities for about two years. Many examples of successful use of this strategy for LF elimination in small- and large-scale trials have been documented in India and several other endemic countries in the world. Implementing DEC-iodine-fortified salt is a safe, less expensive, more efficient and prompt approach for achieving the elimination of LF in India. Adverse effects are none or minor and self-limiting. The DEC-fortified salt strategy can easily piggyback on the existing countrywide deployment of iodized salt under the National Iodine Deficiency Disorders Control Programme (NIDDCP), which has achieved a great success in reducing iodine-deficiency disorders such as hypothyroidism. This existing robust programme can be leveraged to launch DEC-fortified salt for the community. If implemented appropriately, this strategy will ensure the complete cessation of LF transmission within two years from its introduction. If the said strategy is implemented in 2022, it is expected that India will be able to achieve the LF elimination by 2024, much before the global target of 2030.

Knowledge, Attitude and Practice Survey on Special Care Dentistry: A Cross-sectional Study

Introduction: Special Care Dentistry (SCD) is a dentistry branch that advocates equal dental Patient with Special Care Needs (PSCN). In several countries, it is a separate specialty. In India, it is still in its infancy. Few studies have explored the dentists' perception regarding SCD. Aim: To determine the knowledge and attitude about SCD, also the practice measures followed by the dentists in Chennai colleges. Materials and Methods: This cross-sectional observational study was conducted in three dental colleges in Chennai from September 2019 to October 2019. A total of 230 dentists were enrolled using random sampling. A set of 20 close ended multiple choice questions were formulated and administered to dentists {Undergraduates (UGs) and Postgraduates (PGs)}. Descriptive statistics and Chi-square test was performed using MATLAB software (Mathworks, 2015), with p<0.05. Results: A 78.8% of respondents got good scores of ≥7 in knowledge based questions, 25.6% of the participants showed overall positive attitude. Educational qualification did not affect respondents’ knowledge and attitude about SCD (p>0.05). Only 21.95% of UGs and 22.31% of the PGs have good self-confidence in treating patients with special needs. More than 80% have not administered Domiciliary Care (DC). A total of 65% of participants denied getting any training in their UGs/PGs curriculum. Conclusion: Dentists in the present study are aware about SCD. Clinical measures adopted by dentists and their confidence in treating these patients are suboptimal. Training in SCD should become integral part of future dental education.

Determinants of transmission hotspots and filarial infection in households after eight rounds of mass drug administration in India

OBJECTIVES

Lymphatic filariasis (LF) elimination through mass drug administration (MDA) of DEC and albendazole have resulted in very low levels of infection in most endemic districts in India. But small pockets with residual microfilaraemia in the community and antigeneamia in children ('hotspots') are a cause of concern. We aimed to identify the determinants of such transmission hotspots and filarial infection in households using data from 33 communities.

METHODS

The filariasis vector Culex quinquefasciatus was collected from 627 randomly selected households using gravid traps. Parallel data on environmental, entomological, demographical, socio-economical and behavioural factors were analysed to identify the determinants of hotspots and household-level infection.

RESULTS

Hotspots and non-hotspots did not differ significantly in terms of socio-economical and behavioural aspects, but did differ in terms of demographical and environmental factors. Logistic regression revealed that tiled and concrete houses increased the risk of an area being a hotspot by 2.0 and 2.9 times respectively. Presence of Culex breeding habitats was significantly associated with elevated risk of being a hotspot. Proximity of U-drains to a house increased the risk of filarial infection 5.8 times.

CONCLUSIONS

An environment suitable to Culex breeding influences continued transmission despite eight rounds of MDA, particularly in hotspots. Proximity to U-drains increases the risk of infection in households. Implementing localised vector control measures may help interrupt low-level transmission, thereby reducing the risk of resurgence in the absence of MDA.

Simulation based reliability evaluation of AC power supply system of Indian Nuclear Power Plant

Purpose

The purpose of this paper is to demonstrate the potential of simulation approach for performance evaluation in a complex environment with a case of application from Indian Nuclear Power Plant.

Design/methodology/approach

In this work, stochastic simulation approach is applied to availability evaluation of AC Power supply system of Indian Nuclear Power Plant (INPP). In the presently followed test, maintenance policies on diesel generators and circuit breakers are considered to exactly model the practical scenario. System success logic incorporates the functional dependencies and dynamics in the sequence of operations and maintenance policies. In each iteration (random experiment), from simulated random behaviour of the system, uptime and down time are calculated based on system success logic. After sufficient number of iterations, unavailability and other required reliability measures are estimated from the results.

Findings

The subsystems of AC Power Supply System of NPP are having multi‐states due to surveillance tests and scheduled maintenance activities. In addition, the operation of DG involves starting and running (till its mission time) which is a sequential (or conditional) event. Furthermore, the redundancies and dependencies are adding to the complexity.

Originality/value

This paper emphasizes the importance of realistic reliability modelling in complex operational scenario with Monte‐Carlo simulation approach. Simulation procedure for evaluating the availability/reliability of repairable complex engineering systems having stand‐by tested components is presented. The same simulation model finds application in importance measures calculation, technical specification optimization and uncertainty quantification.

Operational feasibility of lot quality assurance sampling (LQAS) as a tool in routine process monitoring of filariasis control programmes

Lot quality assurance sampling (LQAS) with two-stage sampling plan was applied for rapid monitoring of coverage after every round of mass drug administration (MDA). A Primary Health Centre (PHC) consisting of 29 villages in Thiruvannamalai district, Tamil Nadu was selected as the study area. Two threshold levels of coverage were used: threshold A (maximum: 60%; minimum: 40%) and threshold B (maximum: 80%; minimum: 60%). Based on these thresholds, one sampling plan each for A and B was derived with the necessary sample size and the number of allowable defectives (i.e. defectives mean those who have not received the drug). Using data generated through simple random sampling (SRSI) of 1,750 individuals in the study area, LQAS was validated with the above two sampling plans for its diagnostic and field applicability. Simultaneously, a household survey (SRSH) was conducted for validation and cost-effectiveness analysis. Based on SRSH survey, the estimated coverage was 93.5% (CI: 91.7-95.3%). LQAS with threshold A revealed that by sampling a maximum of 14 individuals and by allowing four defectives, the coverage was >or=60% in >90% of villages at the first stage. Similarly, with threshold B by sampling a maximum of nine individuals and by allowing four defectives, the coverage was >or=80% in >90% of villages at the first stage. These analyses suggest that the sampling plan (14,4,52,25) of threshold A may be adopted in MDA to assess if a minimum coverage of 60% has been achieved. However, to achieve the goal of elimination, the sampling plan (9, 4, 42, 29) of threshold B can identify villages in which the coverage is <80% so that remedial measures can be taken. Cost-effectiveness analysis showed that both options of LQAS are more cost-effective than SRSH to detect a village with a given level of coverage. The cost per village was US dollars 76.18 under SRSH. The cost of LQAS was US dollars 65.81 and 55.63 per village for thresholds A and B respectively. The total financial cost of classifying a village correctly with the given threshold level of LQAS could be reduced by 14% and 26% of the cost of conventional SRSH method.

A geostatistical analysis of the geographic distribution of lymphatic filariasis prevalence in southern India

Gaining a better understanding of the spatial population structure of infectious agents is increasingly recognized as being key to their more effective mapping and to improving knowledge of their overall population dynamics and control. Here, we investigate the spatial structure of bancroftian filariasis distribution using geostatistical methods in an endemic region in Southern India. Analysis of a parasite antigenemia prevalence dataset assembled by sampling 79 villages selected using a World Health Organization (WHO) proposed 25 x 25 km grid sampling procedure in a 225 x 225 km area within this region was compared with that of a corresponding microfilaraemia prevalence dataset assembled by sampling 119 randomly selected villages from a smaller subregion located within the main study area. A major finding from the analysis was that once large-scale spatial trends were removed, the antigenemia data did not show evidence for the existence of any small-scale dependency at the study sampling interval of 25 km. By contrast, analysis of the randomly sampled microfilaraemia data indicated strong spatial contagion in prevalence up to a distance of approximately 6.6 kms, suggesting the likely existence of small spatial patches or foci of transmission in the study area occurring below the sampling scale used for sampling the antigenemia data. While this could indicate differences in parasite spatial population dynamics based on antigenemia versus microfilaraemia data, the result may also suggest that the WHO recommended 25 x 25 km sampling grid for rapid filariasis mapping could have been too coarse a scale to capture and describe the likely local variation in filariasis infection in this endemic location and highlights the need for caution when applying uniform sampling schemes in diverse endemic regions for investigating the spatial pattern of this parasitic infection. The present results, on the other hand, imply that both small-scale spatial processes and large-scale factors may characterize the observed distribution of filariasis in the study region. Our preliminary analysis of a mountain range associated large-scale trend in the antigenemia data suggested that a nonlinear relationship of infection prevalence with elevation might be a factor behind such observed global spatial patterns. We conclude that geostatistic methods can provide a powerful framework for carrying out the empirical investigation and analysis of parasite spatial population structure. This study shows that their successful application, however, will crucially depend on our gaining a more thorough understanding of the appropriate geographic scales at which spatial studies should be carried out.

EPIFIL: the development of an age-structured model for describing the transmission dynamics and control of lymphatic filariasis

Mathematical models of transmission dynamics of infectious diseases provide a useful tool for investigating the impact of community based control measures. Previously, we used a dynamic (constant force-of-infection) model for lymphatic filariasis to describe observed patterns of infection and disease in endemic communities. In this paper, we expand the model to examine the effects of control options against filariasis by incorporating the impact of age structure of the human community and by addressing explicitly the dynamics of parasite transmission from and to the vector population. This model is tested using data for Wuchereria bancrofti transmitted by Culex quinquefasciatus in Pondicherry, South India. The results show that chemotherapy has a larger short-term impact than vector control but that the effects of vector control can last beyond the treatment period. In addition we compare rates of recrudescence for drugs with different macrofilaricidal effects.

Cost of mass annual single dose diethylcarbamazine distribution for the large scale control of lymphatic filariasis

Economic analysis of the revised strategy to control lymphatic filariasis with mass annual single dose diethylcarbamazine (DEC) at 6 mg/kg body weight launched in one of the districts of Tamil Nadu in 1996 was carried out. This exploratory study, proposed for five years in 13 districts under 7 states on a pilot scale through the Department of Public Health is an additional input of the existing National Filaria Control Programme in India. A retrospective costing exercise was undertaken systematically from the provider's perspective following the completion of the first round of drug distribution. The major activities and cost components were identified and itemized cost menu was prepared to estimate the direct (financial) and indirect (opportunity) cost related to the implementation of the Programme. The total financial cost of this Programme to cover 22.7 lakh population in the district was Rs. 22.05 lakhs. The opportunity cost of labour and capital investment was calculated to be Rs. 7.98 lakhs. The total per capita cost was Rs. 1.32, with Rs. 0.97 and Rs. 0.35 as financial and opportunity cost respectively. Based on these estimates, the implementation cost of the Programme at Primary Health Centre (PHC) level was calculated and projected for five years. The additional financial cost for the existing health care system is estimated to be Rs. 27,800 per PHC every year. DEC tablets (50 mg) was the major cost component and sensitivity analysis showed that the cost of the Programme could be minimized by 20 per cent by switching over to 100 mg tablets. The analysis indicates that this Programme is a low-cost option and the results are discussed in view of its operational feasibility and epidemiological impact.

Development of rapid assessment procedures for the delimitation of lymphatic filariasis-endemic areas

Lymphatic filariasis caused by Wuchereria bancrofti is a major public health problem in 73 tropical and subtropical countries including India. Delimitation of endemic areas is essential to plan control operations. The current method of night blood survey (NBS) for delimitation is cumbersome, time-consuming and expensive. Therefore, there is a need to develop assessment procedures which can rapidly delimit endemic areas. For this purpose we evaluated three procedures: direct interviewing of key informants using structured questionnaires, an indirect method of a self-administered questionnaires to key informants and physical examination by health workers for the presence of chronic filarial disease. Thirty rural communities in a filariasis-endemic region in Cuddalore district in Tamil Nadu State in southern India constituted the study population. The determination of filariasis endemicity in the village communities assessed by the above procedures was compared in terms of rapidity, specificity, sensitivity and cost with the microfilaria rate and disease rate obtained by night blood sample survey and clinical examination by physicians. Prevalence score, control preference score and weighted mean number of cases with filarial disease per village were calculated using the key informant questionnaire techniques. While the prevalence and control preference score showed low sensitivity and moderate specificity, weighted mean number of cases showed high sensitivity and moderate specificity in identifying endemic villages. The prevalence of disease as determined by the physical examination of a sample population by health workers was highly sensitive in identifying communities endemic for filariasis. The degree of association between the disease rates estimated by physician and trained health workers was significant (r = 0.56; P < 0.05). These observations suggest that the weighted mean number of cases per village obtained through key informant techniques may be considered at a primary level to crudely identify endemic areas, followed by physical examination by health workers for filariasis, since it is relatively cheap and rapid.

Epifil: a dynamic model of infection and disease in lymphatic filariasis

The lack of a quantitative framework that describes the dynamic relationships between infection and morbidity has constrained efforts aimed at the community-level control of lymphatic filariasis. In this paper, we describe the development and validation of EPIFIL, a dynamic model of filariasis infection intensity and chronic disease. Infection dynamics are modeled using the well established immigration-death formulation, incorporating the acquisition of immunity to infective larvae over time. The dynamics of disease (lymphodema and hydrocele) are modeled as a catalytic function of a variety of factors, including worm load and the impact of immunopathological responses. The model was parameterized using age-stratified data collected from a Bancroftian filariasis endemic area in Pondicherry in southern India. The fitted parameters suggest that a relatively simple model including only acquired immunity to infection and irreversible progression to disease can satisfactorily explain the observed infection and disease patterns. Disease progression is assumed to be a consequence of worm induced damage and to occur at a high rate for hydrocele and a low rate for lymphodema. This suggests that immunopathology involvement may not be a necessary component of observed age-disease profiles. These findings support a central role for worm burden in the initiation and progression of chronic filarial disease.

Rapid assessment procedures (RAP) for lymphatic filariasis

BACKGROUND

New strategies are emerging for control of filariasis in terms of chemotherapy and vector control. Field application of these tools requires mapping and prioritization of filaria-endemic areas and quantification of the infection/ disease burden. Available procedures are time-consuming, costly and have poor sensitivity. Therefore, rapid assessment procedures need to be developed to assess the disease burden as well as monitor and evaluate control programmes.

METHODS

Data collected on different variables from 25 areas in India and elsewhere were used. The relationship between prevalence of human infection and vector infection rate was analysed quantitatively. Due to lack of independent samples, only qualitative analysis was carried out between other epidemiological variables such as infection and disease prevalence in relation to age, gender and manifestation.

RESULTS

There was a significant positive correlation between vector infection rate and infection prevalence in humans, suggesting that vector infection can be used as an indicator in the rapid assessment of infection prevalence. Scatter plots showed that community screening may be limited to the age group of 11-30 years for infection prevalence and 20-50 years for disease prevalence. Further, clinical surveys may be limited to only hydrocele prevalence which may be sufficient to predict the total disease. This can also be used as an alternative method by the community itself for delimiting endemic areas.

CONCLUSIONS

Vector infection rate may be used as an indicator for rapid assessment of human infection. Alternatively, blood smear examination could be limited to the age group of 11-30 years. For a rapid survey of the diseases, males in the age group of 20-50 years could be examined only for hydrocele.

Past exposure and the dynamics of lymphatic filariasis infection in young children

This study utilizes parallel, longitudinal entomological and parasitological data collected during a 5-year vector control programme in Pondicherry, South India, to quantify Wuchereria bancrofti transmission from the vector to the human population. A simple mathematical model, derived from the standard catalytic model, is used to examine the hypothesis that current infection prevalence in young children is a dynamical function of their cumulative past exposure to infective bites. Maximum likelihood fits of the model to the observed data indicate a constant child infection rate with age, above a threshold representing the pre-patent period, or equivalently, the cumulative biting intensity required to produce patent infections. Extrapolation of the model allows the crude estimation of the equilibrium microfilaria age-prevalence curve due to control. The results suggest that vector control alone may have little impact on the overall age-prevalence of infection even when sustained for long periods. These observations are discussed in terms of the likely impact of density dependent mechanisms, such as acquired immunity, on model predictions.

Clinical manifestations of bancroftian filariasis with special reference to lymphoedema grading

We report on some aspects of progression of chronic disease and its association with acute manifestations with special reference to grades of lymphoedema in bancroftian filariasis. These analyses were based on the clinical history and clinical findings of 1300 individuals at the time of their first visit to the filariasis clinic at a centre in south India. The mean number of adenolymphangitis (ADL) attacks in one year was 4.9 +/- 1.7, 5.5 +/- 0.9 and 10.4 +/- 3.2 in patients with grade I, grade II and grade III lymphoedema respectively. The mean duration of oedema was 47.4 +/- 5.9 days, 6.2 +/- 0.5 and 8.6 +/- 0.9 yr in patients with grade I, grade II and grade III lymphoedema respectively. These findings suggest that the progression of lymphoedema from one grade to the next in bancroftian filariasis is associated with increased frequency of ADL attacks.

Micro-spatial variation in filarial disease and risk of developing disease associated with microfilaremia in urban situation

Clinical and parasitological surveys were carried out concurrently during 1986 in Pondicherry. The analyses showed that there was no significant micro-spatial variation in prevalence of total diseases (acute and chronic) and the manifestations such as hydrocele and lymphedema in the different zones and stations of Pondicherry urban area, a stable endemic area. Analyses on different filariometric indices in different stations showed a significant correlation between disease and mf prevalence (r = 0.4106; p = 0.037). The prevalence of disease and hydrocele in microfilaremic individuals (9.4% and 20.0% respectively) was higher compared to that observed in amicrofilaremic persons (6.4% and 11.2% respectively). The relative risk (RR) of parasite carriers developing disease (any manifestations) was marginally higher compared to amicrofilaremic persons (1.18). However, the RR of developing hydrocele manifestation due to microfilaremia was much greater (1.5) compared to amicrofilaremic persons. The attributable risk (AR) due to microfilaremia for developing hydrocele was 0.05. This suggests that although the risk is high in mf carriers, there might be alternate ways of developing disease without the infected person becoming microfilaremic. The limitations of point prevalence data on understanding complex dynamics of infection and disease are discussed.

Cumulative exposure and its relationship with chronic filarial disease in bancroftian filariasis

Several hypotheses have been put forth about the factors influencing the dynamics of infection and disease in lymphatic filariasis. However, appropriate validation of these hypotheses by real situation analyses of epidemiological data is lacking. The present analyses examine the relationship between cumulative exposure to infection and prevalence of disease by utilizing the existing entomological and clinical data collected between 1981 and 1986 in Pondicherry, South India, endemic for bancroftian filariasis. While there was a significant negative association when the cumulative exposure was correlated with total prevalence of disease (r = 0.70, p = 0.024) as well as hydrocele alone (r = 0.74, p = 0.014), a significant positive association was found with prevalence of lymphedema (r = 0.72, p = 0.018). These results suggest that hydrocele development follows early after exposure, but prolonged exposure could result either in development of lymphedema or immune tolerance resulting in microfilaremia. These could also suggest that the pathomechanisms in development of hydrocele and lymphedema could follow different pathways. Implications of the present findings are discussed in light of the various hypotheses put forward by earlier studies.

Utility of the force of infection model for assessing changes in the dynamics of bancroftian filarial infections

Force of infection is measured in terms of the number of effective contacts that have been introduced into the population by infective vectors. The utility of such a measure in describing the dynamics of bancroftian filarial infection was tested. Force of infection (beta) incorporating the durations of patent period and pre-patent period was estimated for different age classes (assuming that it is constant in that particular age class) and it was found that the predicted post-control prevalences were close to the observed figures. Utility of Remme's model in areas with different transmission levels is discussed. It was examined whether the empirical function generally used in helminth infections to describe the functional relationship between beta and age could be used for lymphatic filariasis. The relationship between the two was not adequately described by the function. Force of infection, when compared with rate of acquisition calculated using longitudinal data, showed that this measure could be used as a crude estimate of rate of acquisition in places which do not have longitudinal data sets.

Filariasis and blood groups

BACKGROUND

Using modern statistical techniques, we investigated the controversial relationship between lymphatic filariasis and blood groups in a very large number of patients.

METHODS

The ABO blood group, microfilaraemia and symptomatic disease status of 1444 persons was determined. The association between the filarial status and ABO blood group was studied by the Chi-square test and the method of logistic regression by fitting a model. This method simultaneously tested for association of factors such as blood groups and age with the occurrence of parasitaemia or filarial disease.

RESULTS

The ABO blood groups were not risk factors in the occurrence of patent parasitaemia or filarial disease though age was associated with the occurrence of microfilaraemia and symptomatic disease.

CONCLUSION

ABO blood groups are not associated with the occurrence of bancroftian filariasis.

Frequency distribution of Brugia malayi microfilariae in human populations

This study examines the effects of host age and sex on the frequency distribution of Brugia malayi infections in the human host. Microfilarial (mf) counts for a large data base on the epidemiology of brugian filariasis in Shertallai, Kerala, South India are analysed. Frequency distributions of microfilarial counts partitioned by age are successfully described by zero-truncated negative binomial distributions, fitted by maximum likelihood. This analysis provides estimates of the proportion of mf-positive individuals who are identified as negative due to sampling errors, allowing the construction of corrected mf age-prevalence curves, which indicate that the observed prevalence may under-estimate the true figures by between 18 and 47%. There is no evidence from these results for a decrease in the degree of over-dispersion of parasite frequency distributions with host age, such as might be produced by the acquired immunity to infection. This departure from the pattern in bancroftian filariasis (where there is evidence of such decreases in over-dispersion; Das et al. 1990) is discussed in terms of the long history of filariasis control (and consequently low infection prevalence) in Shertallai.

The dynamics of infection and disease in bancroftian filariasis

This study examines the relationship between the dynamic of Wuchereria bancrofti infection and the development of chronic lymphatic disease. Data sets from Pondicherry, south India, and Calcutta are used to estimate the age-specific proportion of the endemic population which has converted from microfilaria positive to amicrofilaraemia, and is assumed to be at risk of disease. For men, but not women, the age-prevalence profile of the estimated population 'at risk' is shown to correspond closely to the observed age-prevalence of chronic lymphatic disease in the same community. For both sexes, and independent of age, approximately 11% of the population at risk eventually develop lymphoedema. These observations suggest that filariasis endemic populations consist of those individuals who remain amicrofilaraemic and asymptomatic, and those who progress through the sequence: uninfected, microfilaraemic, amicrofilaraemic, to develop irreversible obstructive lymphatic pathology.

Clinical epidemiology of bancroftian filariasis: effect of age and gender

A cross-sectional survey was used to determine the prevalence of disease (n = 6493) and microfilaraemia (n = 24,946) due to Wuchereria bancrofti in Pondicherry, south India. The total disease attributable to filariasis was significantly higher in males (13.67%) than females (2.26%), due to the occurrence of hydrocele in males. While the prevalence of chronic signs was clearly age-dependent in both sexes, that of acute signs was independent of age. Thus the age and gender structure of the survey sample will crucially influence apparent prevalence. Examination of the gender differences in the point prevalence of disease in 12 areas of India showed a significant relationship between occurrence of disease and gender, but this relationship did not significantly differ between northern and southern Indian populations. The study suggested that the failure to appreciate the importance of age and gender in disease prevalence has led to misconception about disease patterns in India.

Clinical manifestations of bancroftian filariasis in relation to microfilaraemia and diethylcarbamazine therapy

We studied the clinical manifestations of Bancroftian filariasis in relation to microfilaraemia and diethylcarbamazine (DEC) therapy in three groups of individuals in Pondicherry. In 3170 persons examined in a door-to-door survey (Group I), the prevalence of disease was found to be independent of microfilaria (mf) status (the disease rate was 13.4% in mf carriers and 13.6% in amicrofilaraemic persons). There was no association between the occurrence of disease (and individual manifestations), and mf status and its intensity in 1103 mf carriers examined in the filariasis clinic (Group II). Clinical manifestations, however, were age and sex dependent in Group II. Change in mf status in a five-year period (1981 to 1986) with and without DEC therapy did not influence the clinical manifestations in 1024 individuals (Group III). Though the disease rate in mf carriers who discontinued DEC (22.2%) and in those who completed one course of DEC (14.8%) was higher than those who did not receive DEC (10.6%), statistical analysis did not show any significant difference between the groups. The study confirms that the dynamics of infection and filarial disease are complex, and other associated factors need to be investigated.

Frequency distribution of Wuchereria bancrofti microfilariae in human populations and its relationships with age and sex

This paper examines the effects of host age and sex on the frequency distribution of Wuchereria bancrofti infections in the human host. Microfilarial counts from a large data base on the epidemiology of bancroftian filariasis in Pondicherry, South India are analysed. Frequency distributions of microfilarial counts divided by age are successfully described by zero-truncated negative binomial distributions, fitted by maximum likelihood. Parameter estimates from the fits indicate a significant trend of decreasing overdispersion with age in the distributions above age 10; this pattern provides indirect evidence for the operation of density-dependent constraints on microfilarial intensity. The analysis also provides estimates of the proportion of mf-positive individuals who are identified as negative due to sampling errors (around 5% of the total negatives). This allows the construction of corrected mf age-prevalence curves, which indicate that the observed prevalence may underestimate the true figures by between 25% and 100%. The age distribution of mf-negative individuals in the population is discussed in terms of current hypotheses about the interaction between disease and infection.