Community-based Active Surveillance Research Articles

Plasmodium gametocyte carriage in humans and sporozoite rate in anopheline mosquitoes in Gondar zuria district, Northwest Ethiopia.

Although the overall burden of malaria is decreasing in Ethiopia, a recent report of an unpredictable increased incidence may be related to the presence of community-wide gametocyte-carrier individuals and a high proportion of infected vectors. This study aimed to reveal the current prevalence of gametocyte-carriage and the sporozoite infectivity rate of Anopheles vectors for Plasmodium parasites. A community-based cross-sectional study was conducted from May 01 to June 30/2019. A total of 53 households were selected using systematic random sampling and a 242 study participants were recruited. Additionally,515 adult female Anopheles mosquitoes were collected using Center for Diseases Control and Prevention (CDC) light traps and mouth aspirators. Parasite gametocytemia was determined using giemsa stain microscopy, while sporozoite infection was determined by giemsa staining microscopy and enzyme linked immunosorbent assay (ELISA). Among the total 242 study participants, 5.4% (95%, CI = 2.9-8.3) of them were positive for any of the Plasmodium species gametocyte. Furthermore, being female [AOR = 15.5(95%, CI = 1.71-140.39)], age group between 15-29 years old [AOR = 16.914 (95%, CI = 1.781-160.63)], no ITNs utilization [AOR = 16.7(95%, CI = 1.902 -146.727)], and high asexual parasite density [(95%, CI = 0.057-0.176, P = 0.001, F = 18.402)] were identified as statistically significant factors for gametocyte carriage. Whereas sporozoite infection rate was 11.6% (95%, CI = 8.2-15.5) and 12.7% (95%, CI = 9.6-16.3) by microscopy and ELISA, respectively. Overall, this study indicated that malaria remains to be an important public health problem in Gondar Zuria district where high gametocyte carriage rate and sporozoite infection rate could sustain its transmission and burden. Therefore, in Ethiopia, where malaria elimination program is underway, frequent, and active community-based surveillance of gametocytemia and sporozoite infection rate is important.

Pertussis outbreak investigation in south Gondar zone, Northwest, Ethiopia

Aims: Pertussis, also known as whooping cough, is a highly contagious respiratory infection caused by the bacterium Bordetella pertussis. Though vaccines are the most successful and cost-effective way of preventing pertussis, the outbreak of pertussis is still high in the Amhara region. The study aimed to investigate the pertussis infection in Simada district, North West Ethiopia, 2021. Methods: A community-based active surveillance was conducted in the Simada district from December 3/2020 to January 05/2021. A total of 43 cases was identified using the modified Centers for Disease Control and Prevention (CDC) pertussis diagnosis criteria and line lists. The collected data were entered into the Epi-data (Epidemiological Data) version 3.1 and analyzed using R version 4.03 software and descriptive statistics computed. Results: A total of 43 cases were identified with an overall attack rate of 7.1 per 1000 population. All complicated cases occurred in children under four years of age. The most affected groups were females. There was an interrupted routine immunization service in the cluster at the health post-level to associate vaccination coverage with the occurrence of a pertussis outbreak. The outbreak was reported after three days of the occurrence of more transmission from person to person. Conclusion: The outbreak of pertussis was high and the children were suffering. It is advisable to build capacity, consolidate routine vaccination services, and enhancing the vaccine cold chain management system, surveillance and early treatment of infected patients to control the expansion of pertussis.

Curbing an outbreak of circulating vaccine derived poliovirus type 2 in Dollo Zone, Somali Region, Ethiopia: response to outbreak.

Introductionalthough the oral polio vaccine prevents virus transmission from person to person, it is crucial for poliovirus eradication. The continued use of live attenuated poliovirus poses an ongoing risk of circulating Vaccine Derived Poliovirus-2 (cVDPV2) outbreaks. This study assesses the response to the cVDPV2 outbreak in Dollo Zone, Somali Region, Ethiopia.Methodsafter examining and verifying the occurrence of the outbreak, a team was established and prepared by resource mobilization, advocacy, and social mobilization. The group endorsed a four-step vaccination strategy, first the rapid response within 14-days by vaccinating a monovalent oral poliovirus-2 (mOPV2) to all under 5-year children in the Zone. The team further enhanced Supplementary Immunization Activities (SIA) for all under-five children with repeated doses of vaccines. At the same time, the team initiated community-based surveillance of Acute Flaccid Paralysis (AFP).Resultsin the rapid-response immunization, an average of 91.4% of 0-11 months old and 90.2% of 12-59 months children were vaccinated. In SIA-1, the team vaccinated an average of 88% and 97%, and in SIA-2, 94.8% and 97.6% of children 0-11 months old and 12-59 months old, respectively. The active community-based surveillance of AFP revealed the existence of the disease in a sporadic form, of which two cases were found in Bokh district.Conclusionthe response to curb the outbreak of cVDPV2 has shown a flow of actions to combat the outbreak. Strengthening and formation of response teams at different levels, resource mobilization, advocacy, and social mobilization are all essential components in maximizing the response to the outbreak.

Senegal, a new potential endemic country for Buruli ulcer?

Mycobacterium ulcerans is the causal agent of Buruli ulcer, a neglected tropical disease with cutaneous tropism. We report a case of Buruli ulcer in a patient who travelled in Senegal, a country not identified by the World Health Organization as being endemic for this disease. This case is the third case of Buruli ulcer reported as having been contracted in Senegal, showing the urgent need to develop data collection in this country by having an active community-based surveillance–response system.

Implementing active community-based surveillance-response system for Buruli ulcer early case detection and management in Ghana.

BackgroundBuruli Ulcer (BU) is one of the most neglected debilitating tropical diseases caused by Mycobacterium ulcerans, which causes considerable morbidity and disability. Building on earlier findings that community-based interventions could enhance case detection and reduce treatment dropout and defaulter rates, we established an active surveillance-response system in an endemic sub-district in the Ga West municipality of Ghana to enhance early case detection, diagnosis and treatment to reduce or eliminate severe ulcers and its related disabilities.MethodsWe established surveillance response system, implemented in collaboration with the sub-district disease control officers, selected clinical staff and trained community-based volunteers. The active community-based surveillance- response system was implemented for 12 months. Also, pre and post intervention surveys were conducted to document any change in perceptions on BU in the study population over the period. The baseline and endline surveys were conducted in August 2016 and August 2017 respectively.ResultsOn average, each person was seen 11 times in 12 months. In all 75 skin lesions were detected during surveillance rounds, out of which 17 were suspected to be BU and 12 out of the 17 were confirmed as BU using Polymerase chain reaction (PCR). Out of the 12, five, three and four were categories I, II and III lesions respectively. Physical examination was done on 94% of the people seen during the surveillance rounds. Knowledge on BU has also increased in the communities at the end of the study.ConclusionThe findings from this study have demonstrated that it is possible to establish surveillance-response system for BU and by extension, other neglected tropical diseases to enhance control and elimination efforts through the use of community-based volunteers.

Burden of Influenza in 4 Ecologically Distinct Regions of Peru: Household Active Surveillance of a Community Cohort, 2009-2015.

There are limited data on the burden of disease posed by influenza in low- and middle-income countries. Furthermore, most estimates of influenza disease burden worldwide rely on passive sentinel surveillance at health clinics and hospitals that lack accurate population denominators. We documented influenza incidence, seasonality, health-system utilization with influenza illness, and vaccination coverage through active community-based surveillance in 4 ecologically distinct regions of Peru over 6 years. Approximately 7200 people in 1500 randomly selected households were visited 3 times per week. Naso- and oropharyngeal swabs were collected from persons with influenza-like illness and tested for influenza virus by real-time reverse-transcription polymerase chain reaction. We followed participants for 35353 person-years (PY). The overall incidence of influenza was 100 per 1000 PY (95% confidence interval [CI], 97-104) and was highest in children aged 2-4 years (256/1000 PY [95% CI, 236-277]). Seasonal incidence trends were similar across sites, with 61% of annual influenza cases occurring during the austral winter (May-September). Of all participants, 44 per 1000 PY (95% CI, 42-46) sought medical care, 0.7 per 1000 PY (95% CI, 0.4-1.0) were hospitalized, and 1 person died (2.8/100000 PY). Influenza vaccine coverage was 27% among children aged 6-23 months and 26% among persons aged ≥65 years. Our results indicate that 1 in 10 persons develops influenza each year in Peru, with the highest incidence in young children. Active community-based surveillance allows for a better understanding of the true burden and seasonality of disease that is essential to plan the optimal target groups, timing, and cost of national influenza vaccination programs.

Epidemiology of Pertussis Among Young Pakistani Infants: A Community-Based Prospective Surveillance Study.

Background. Pertussis remains a cause of morbidity and mortality among young infants. There are limited data on the pertussis disease burden in this age group from low- and lower-middle-income countries, including in South Asia.Methods. We conducted an active community-based surveillance study from February 2015 to April 2016 among 2 cohorts of young infants in 4 low-income settlements in Karachi, Pakistan. Infants were enrolled either at birth (closed cohort) or at ages up to 10 weeks (open cohort) and followed until 18 weeks of age. Nasopharyngeal swab specimens were obtained from infants who met a standardized syndromic case definition and tested for Bordetella pertussis using real-time polymerase chain reaction. We determined the incidence of pertussis using a protocol-defined case definition, as well as the US Centers for Disease Control and Prevention (CDC) definitions for confirmed and probable pertussis.Results. Of 2021 infants enrolled into the study, 8 infants met the protocol-defined pertussis case definition, for an incidence of 3.96 (95% confidence interval [CI], 1.84–7.50) cases per 1000 infants. Seven of the pertussis cases met the CDC pertussis case definition (5 confirmed, 2 probable), for incidences of CDC-defined confirmed pertussis of 2.47 (95% CI, .90–5.48) cases per 1000 infants, and probable pertussis of 0.99 (95% CI, .17–3.27) cases per 1000 infants. Three of the pertussis cases were severe according to the Modified Preziosi Scale score.Conclusions. In one of the first prospective surveillance studies of infant pertussis in a developing country, we identified a moderate burden of pertussis disease in early infancy in Pakistan.

Incidence of Dengue Virus Infection in Adults and Children in a Prospective Longitudinal Cohort in the Philippines.

BackgroundThe mean age of dengue has been increasing in some but not all countries. We sought to determine the incidence of dengue virus (DENV) infection in adults and children in a prospective cohort study in the Philippines where dengue is hyperendemic.Methodology/Principal FindingsA prospective cohort of subjects ≥6 months old in Cebu City, Philippines, underwent active community-based surveillance for acute febrile illnesses by weekly contact. Fever history within the prior seven days was evaluated with an acute illness visit followed by 2, 5, and 8-day, and 3-week convalescent visits. Blood was collected at the acute and 3-week visits. Scheduled visits took place at enrolment and 12 months that included blood collections. Acute samples were tested by DENV PCR and acute/convalescent samples by DENV IgM/IgG ELISA to identify symptomatic infections. Enrolment and 12-month samples were tested by DENV hemagglutination inhibition (HAI) assay to identify subclinical infections. Of 1,008 enrolled subjects, 854 completed all study activities at 12 months per-protocol undergoing 868 person-years of surveillance. The incidence of symptomatic and subclinical infections was 1.62 and 7.03 per 100 person-years, respectively. However, in subjects >15 years old, only one symptomatic infection occurred whereas 27 subclinical infections were identified. DENV HAI seroprevalence increased sharply with age with baseline multitypic HAIs associated with fewer symptomatic infections. Using a catalytic model, the historical infection rate among dengue naïve individuals was estimated to be high at 11–22%/year.Conclusions/SignificanceIn this hyperendemic area with high seroprevalence of multitypic DENV HAIs in adults, symptomatic dengue rarely occurred in individuals older than 15 years. Our findings demonstrate that dengue is primarily a pediatric disease in areas with high force of infection. However, the average age of dengue could increase if force of infection decreases over time, as is occurring in some hyperendemic countries such as Thailand.

High rate of subclinical chikungunya virus infection and association of neutralizing antibody with protection in a prospective cohort in the Philippines.

BackgroundChikungunya virus (CHIKV) is a globally re-emerging arbovirus for which previous studies have indicated the majority of infections result in symptomatic febrile illness. We sought to characterize the proportion of subclinical and symptomatic CHIKV infections in a prospective cohort study in a country with known CHIKV circulation.Methods/FindingsA prospective longitudinal cohort of subjects ≥6 months old underwent community-based active surveillance for acute febrile illness in Cebu City, Philippines from 2012-13. Subjects with fever history were clinically evaluated at acute, 2, 5, and 8 day visits, and at a 3-week convalescent visit. Blood was collected at the acute and 3-week convalescent visits. Symptomatic CHIKV infections were identified by positive CHIKV PCR in acute blood samples and/or CHIKV IgM/IgG ELISA seroconversion in paired acute/convalescent samples. Enrollment and 12-month blood samples underwent plaque reduction neutralization test (PRNT) using CHIKV attenuated strain 181/clone25. Subclinical CHIKV infections were identified by ≥8-fold rise from a baseline enrollment PRNT titer <10 without symptomatic infection detected during the intervening surveillance period. Selected CHIKV PCR-positive samples underwent viral isolation and envelope protein-1 gene sequencing. Of 853 subjects who completed all study procedures at 12 months, 19 symptomatic infections (2.19 per 100 person-years) and 87 subclinical infections (10.03 per 100 person-years) occurred. The ratio of subclinical-to-symptomatic infections was 4.6:1 varying with age from 2:1 in 6 month-5 year olds to 12:1 in those >50 years old. Baseline CHIKV PRNT titer ≥10 was associated with 100% (95%CI: 46.1, 100.0) protection from symptomatic CHIKV infection. Phylogenetic analysis demonstrated Asian genotype closely related to strains from Asia and the Caribbean.ConclusionsSubclinical infections accounted for a majority of total CHIKV infections. A positive baseline CHIKV PRNT titer was associated with protection from symptomatic CHIKV infection. These findings have implications for assessing disease burden, understanding virus transmission, and supporting vaccine development.

High rate of A(H1N1)pdm09 infections among rural Thai villagers, 2009-2010.

BackgroundPandemic influenza A(H1N1)pdm09 emerged in Thailand in 2009. A prospective longitudinal adult cohort and household transmission study of influenza-like illness (ILI) was ongoing in rural Thailand at the time of emergence. Symptomatic and subclinical A(H1N1)pdm09 infection rates in the cohort and among household members were evaluated.MethodsA cohort of 800 Thai adults underwent active community-based surveillance for ILI from 2008–2010. Acute respiratory samples from ILI episodes were tested for A(H1N1)pdm09 by qRT-PCR; acute and 60-day convalescent blood samples were tested by A(H1N1)pdm09 hemagglutination inhibition assay (HI). Enrollment, 12-month and 24-month follow-up blood samples were tested for A(H1N1)pdm09 seroconversion by HI. Household members of influenza A-infected cohort subjects with ILI were enrolled in household transmission investigations in which day 0 and 60 blood samples and acute respiratory samples were tested by either qRT-PCR or HI for A(H1N1)pdm09. Seroconversion between annual blood samples without A(H1N1)pdm09-positive ILI was considered as subclinical infection.ResultsThe 2-yr cumulative incidence of A(H1N1)pdm09 infection in the cohort in 2009/2010 was 10.8% (84/781) with an annual incidence of 1.2% in 2009 and 9.7% in 2010; 83.3% of infections were subclinical (50% in 2009 and 85.9% in 2010). The 2-yr cumulative incidence was lowest (5%) in adults born ≤1957. The A(H1N1)pdm09 secondary attack rate among household contacts was 47.2% (17/36); 47.1% of these infections were subclinical. The highest A(H1N1)pdm09 secondary attack rate among household contacts (70.6%, 12/17) occurred among children born between 1990 and 2003.ConclusionSubclinical A(H1N1)pdm09 infections in Thai adults occurred frequently and accounted for a greater proportion of all A(H1N1)pdm09 infections than previously estimated. The role of subclinical infections in A(H1N1)pdm09 transmission has important implications in formulating strategies to predict and prevent the spread of A(H1N1)pdm09 and other influenza virus strains.

Logistics of Guinea worm disease eradication in South Sudan.

From 2006 to 2012, the South Sudan Guinea Worm Eradication Program reduced new Guinea worm disease (dracunculiasis) cases by over 90%, despite substantial programmatic challenges. Program logistics have played a key role in program achievements to date. The program uses disease surveillance and program performance data and integrated technical–logistical staffing to maintain flexible and effective logistical support for active community-based surveillance and intervention delivery in thousands of remote communities. Lessons learned from logistical design and management can resonate across similar complex surveillance and public health intervention delivery programs, such as mass drug administration for the control of neglected tropical diseases and other disease eradication programs. Logistical challenges in various public health scenarios and the pivotal contribution of logistics to Guinea worm case reductions in South Sudan underscore the need for additional inquiry into the role of logistics in public health programming in low-income countries.

Visceral Leishmaniasis Eradication is a Reality: Data from a Community-based Active Surveillance in Bangladesh

More than 20 million people in Bangladesh are considered at risk of developing visceral leishmaniasis (VL). A community-based active surveillance was conducted in eight randomly selected villages in a highly endemic area of Bangladesh from 2006 to 2008. A total of 6,761 individuals living in 1,550 mud-walled houses were included in the active surveillance. Rapid rK39 dipstick tests were conducted throughout the study period to facilitate the case diagnosis. Individuals with previous or current clinical leishmaniasis were identified on the basis of the case definition of the VL elimination program. Untreated cases of suspected VL were referred to the hospital for treatment. Socioeconomic and environmental information including bed net use was also collected. In 2006, the annual incidence of clinical leishmaniasis in the study area was 141.9 cases per 10,000 population, which was significantly increased by the following year owing to community-based active surveillance for case detection and reporting. However, early case detection and early referral for treatment led to a significant decrease in incidence in 2008. This study suggests that community-based active surveillance using a simple diagnostic tool might play a role in achieving the goal of the VL elimination program.

Varicella in Infants After Implementation of the US Varicella Vaccination Program

To describe varicella disease in infants since implementation of the varicella vaccination program in the United States. From 1995 to 2008, demographic, clinical, and epidemiologic data on cases of varicella in infants were collected prospectively through a community-based active surveillance project. We examined disease patterns for infants in 2 age groups: 0 to 5 and 6 to 11 months. Infant varicella disease incidence declined 89.7% from 1995 to 2008. Infants aged 0 to 5 months had milder clinical disease than those aged 6 to 11 months: ≥50 lesions, 49% vs 58% (P = .038); fever (body temperature > 38°C), 12% vs 21% (P = .014); and varicella-related complications, 6% vs 14% (P = .009), respectively. Age was an independent predictor of the occurrence of complications. The varicella vaccination program has resulted in substantial indirect benefits for infants, who are not eligible for vaccination. Presence of maternal varicella-zoster virus antibodies might explain attenuated disease in very young infants likely born to mothers with history of varicella. Although varicella disease incidence has declined, exposure to varicella-zoster virus continues to occur. Improving varicella vaccination coverage in all age groups will further reduce the risk of varicella exposure and protect those not eligible for varicella vaccination.

Under-recognition and reporting of dengue in Cambodia: a capture–recapture analysis of the National Dengue Surveillance System

Robust disease burden estimates are important for decision-making concerning introduction of new vaccines. Dengue is a major public health problem in the tropics but robust disease burden estimates are lacking. We conducted a two-sample, capture-recapture study in the largest province in Cambodia to determine disease under-recognition to the National Dengue Surveillance System (NDSS). During 2006-2008, community-based active surveillance for acute febrile illness was conducted in 0- to 19-year-olds in rural and urban areas combined with testing for dengue virus infection. Of 14 354 individuals under active surveillance (22 498 person-seasons), the annual incidence ranged from 13·4 to 57·8/1000 person-seasons. During the same period, NDSS incidence rates ranged from 1·1/1000 to 5·7/1000, which was 3·9- to 29·0-fold lower than found in the capture-recapture study. In hospitalized cases, the rate of under-recognition was 1·1- to 2·4-fold. This study shows the substantial degree of under-recognition/reporting of dengue and that reported hospitalized cases are not a good surrogate for estimating dengue disease burden.

Comparison of Rapid Malaria Test and Laboratory Microscopy Investigation for Community-Based Active Surveillance of Asymptomatic Falciparum Malaria in Yenagoa, Niger Delta, Nigeria

Dr Oboro VO 11.9999 Normal 0 false false false MicrosoftInternetExplorer4 Blood samples collected from 272 volunteers in two communities of Bayelsa State in the Niger Delta area were investigated for falciparum malaria parasite using the rapid test based on the detection of soluble antigen and laboratory microscopy test. The data showed that out of the 272 samples collected, 40(14.7%) falciparum malaria cases were identified by microscopic examination. 53(19.5%) were detected by rapid test. The Global (p.f) malaria test kit yielded 22 false negative and 35 false positive results when compared with microscopic findings. Only 18 cases shows true positive results. The specificity and sensitivity of the kit was 80% and 45% respectively when the parasite density is below 100 parasite/ µl. These results shows that rapid test would not give justifiable results as most of the low parasite density cases could escape detection, therefore, it cannot replace laboratory microscopic diagnosis in an active malaria surveillance programme in the study area. Therefore, regulatory agencies should insist on regular laboratory microscopic diagnosis in the surveillance of malaria.

The Incidence and Clinical Characteristics of Herpes Zoster Among Children and Adolescents After Implementation of Varicella Vaccination

The varicella-zoster virus (VZV) vaccine strain may reactivate to cause herpes zoster. Limited data suggest that the risk of herpes zoster in vaccinated children could be lower than in children with naturally acquired varicella. We examine incidence trends, risk and epidemiologic and clinical features of herpes zoster disease among children and adolescents by vaccination status. Population-based active surveillance was conducted among <20 years old residents in Antelope Valley, California, from 2000 through 2006. Structured telephone interviews collected demographic, varicella vaccination and disease histories, and clinical information. From 2000 to 2006, the incidence of herpes zoster among children<10 years of age declined by 55%, from 42 cases reported in 2000 (74.8/100,000 persons; 95% confidence interval [95% CI]: 55.3-101.2) to 18 reported in 2006 (33.3/100,000; 95% CI: 20.9-52.8; P<0.001). During the same period, the incidence of herpes zoster among 10- to 19-year-olds increased by 63%, from 35 cases reported in 2000 (59.5/100,000 persons; 95% CI: 42.7-82.9) to 64 reported in 2006 (96.7/100,000; 95% CI: 75.7-123.6; P<0.02). Among children aged<10 years, those with a history of varicella vaccination had a 4 to 12 times lower risk for developing herpes zoster compared with children with history of varicella disease. Varicella vaccine substantially decreases the risk of herpes zoster among vaccinated children and its widespread use will likely reduce overall herpes zoster burden in the United States. The increase in herpes zoster incidence among 10- to 19-year-olds could not be confidently explained and needs to be confirmed from other data sources.

Uncovering Pneumococcal Disease Burden in Bangladesh

Uncovering Pneumococcal Disease Burden in Bangladesh

Prevalence and Risk of Plasmodium falciparum and P. vivax Malaria among Pregnant Women Living in the Hypoendemic Communities of the Peruvian Amazon

The Amazon region of Iquitos, Peru is hypoendemic for Plasmodium vivax and P. falciparum. There is limited information regarding the epidemiology of malaria during pregnancy in this region. Passive surveillance for clinical malaria among pregnant women was conducted in eight health posts in 2004 and 2005. Community-based active surveillance was conducted to determine the incidence of malarial infection among pregnant women in the community of Zungarococha in 2004 and 2005. Passive surveillance demonstrated that pregnant women had a prevalence of clinical malaria of 7.5% in 2004 and 6.6% in 2005 compared with 20.6% and 22.4% of the total population. Active surveillance showed that pregnant women were 2.3 (95% confidence interval = 1.32-3.95, P = 0.004) times more likely to have a P. falciparum infection compared with non-pregnant women. This study demonstrated that because of detection bias, passive surveillance underestimates the burden of malarial infection during pregnancy, and that subclinical malarial infections may occur frequently among pregnant women in this region. Furthermore, pregnant women in this low-transmission and P. vivax-dominant setting, experience an increased risk for P. falciparum infection, but not P. vivax infection.

Effects of misclassification of causes of death on the power of a trial to assess the efficacy of a pneumococcal conjugate vaccine in The Gambia.

A reduction in cause-specific mortality may be the most important public health measure of the efficacy of a new vaccine. However, in developing countries, assignment of causes of deaths occurring outside hospitals can be assessed often only through the questioning of relatives about the signs and symptoms leading to death ('post-mortem questionnaire'). Causes assigned in this way have poor sensitivity and specificity. We illustrate the effects of this misclassification on the power of a large trial of a pneumococcal polysaccharide/protein conjugate vaccine with a mortality endpoint. Required sample sizes to achieve a study with specified power were calculated for all-cause and acute lower respiratory tract infection (ALRI) mortality for different levels of sensitivity and specificity of post-mortem questionnaires. Data from active community-based surveillance and post-mortem questionnaires collected 1989-1993 from the study area were used in the calculations. The mortality rate among children aged 6-29 months from all causes was 34.2 per 1000 child-years; 19% of deaths were attributable to ALRI. Assuming that pneumococci would be responsible for 50% of ALRI deaths and that the vaccine would cover 70% of disease serotypes and would be 90% effective against these serotypes, the expected efficacy of the vaccine would be 6.0% (19% x 50% x 70% x 90%) against all causes combined and 31.5% (50% x 70% x 90%) against deaths from ALRI. If, as suggested by various reports, the sensitivity and specificity of assigning a death to ALRI by post-mortem questionnaire are about 40% and 90% respectively, then the observed vaccine efficacy against ALRI (as classified using the post-mortem questionnaire) would fall to 20%, and the power to detect this would be reduced by approximately 40%. Furthermore, low sensitivity of diagnosis would lead to a falsely low estimate of the burden of ALRI mortality in the population and the trial might have greater power to detect a reduction in mortality from all causes combined than that estimated at the outset. Low sensitivity and specificity of diagnosis by post-mortem questionnaire may mean that the power of a trial to detect a reduction in all-cause mortality is similar to that to detect a reduction in ALRI mortality. Since the latter is more susceptible to bias from misclassification of cause of death, all-cause mortality may be the most suitable endpoint. Similar considerations apply to trials of interventions against other diseases for which a cause-specific endpoint is subject to substantial misclassification.

Community-based active surveillance for rabies in Machakos District, Kenya

The rabies problem in Kenya has been greatest in Machakos District where the disease has persisted endemically for over 40 years. This paper presents the results of a one-year community-based active surveillance for rabies in six randomly selected sublocations in the district for the period 1992–1993. Approximately 860 rabid dogs per 100 000 dogs were confirmed in this study, compared to approximately 12 per 100 000 confirmed rabid dogs reported by the existing passive-surveillance system. This active surveillance underestimated the true rabies incidence, because only 41% (130/317) of the potential specimens could be diagnosed. Dogs accounted for 92% (179/194) of primary animal-rabies suspects, 80% (66/83) of secondary suspects, and 81% of the confirmed animal-rabies cases. The annual incidence of animal-bites of humans was 234 per 100 000 people and the point estimate of human-rabies incidence per year was 25 per million people. Almost all (97%) animal-bites of humans were due to dogs. The traditional passive-surveillance system grossly underestimated the importance of rabies as a public-health problem in Machakos District. Community-based active surveillance provides a potential cost-effective strategy for greatly improving estimates of rabies incidence and epidemiology to inform veterinary and policy decision-making.