Infected Index Cases Research Articles

Modeling outbreaks of COVID-19 in China: The impact of vaccination and other control measures on curbing the epidemic

ABSTRACT This study aims to examine the development trend of COVID-19 in China and propose a model to assess the impacts of various prevention and control measures in combating the COVID-19 pandemic. Using COVID-19 cases reported by the National Health Commission of China from January 2, 2020, to January 2, 2022, we established a Susceptible-Exposed-Infected-Asymptomatic-Quarantined-Vaccinated-Hospitalized-Removed (SEIAQVHR) model to calculate the COVID-19 transmission rate and Rt effective reproduction number, and assess prevention and control measures. Additionally, we built a stochastic model to explore the development of the COVID-19 epidemic. We modeled the incidence trends in five outbreaks between 2020 and 2022. Some important features of the COVID-19 epidemic are mirrored in the estimates based on our SEIAQVHR model. Our model indicates that an infected index case entering the community has a 50%–60% chance to cause a COVID-19 outbreak. Wearing masks and getting vaccinated were the most effective measures among all the prevention and control measures. Specifically targeting asymptomatic individuals had no significant impact on the spread of COVID-19. By adjusting prevention and control parameters, we suggest that increasing the rates of effective vaccination and mask-wearing can significantly reduce COVID-19 cases in China. Our stochastic model analysis provides a useful tool for understanding the COVID-19 epidemic in China.

A Prospective Study of Key Correlates for Household Transmission of Severe Acute Respiratory Syndrome Coronavirus 2.

Randomized controlled trials evaluated monoclonal antibodies for the treatment (Study 2067) and prevention (Study 2069) of coronavirus disease 2019 (COVID-19). Household contacts of the infected index case in Study 2067 were enrolled in Study 2069 and prospectively followed; these cohorts provided a unique opportunity to evaluate correlates of transmission, specifically viral load. This post hoc analysis was designed to identify and evaluate correlates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission, adjusting for potential confounding factors related to source SARS-CoV-2 viral load and risk of SARS-CoV-2 acquisition in this population. Correlates of transmission were evaluated in potential transmission pairs (any infected household member plus susceptible household contact). In total, 943 participants were included. In multivariable regression, 2 potential correlates were determined to have a statistically significant (P < .05) association with transmission risk. A 10-fold increase in viral load was associated with a 40% increase in odds of transmission; sharing a bedroom with the index participant was associated with a 199% increase in odds of transmission. In this prospective, post hoc analysis that controlled for confounders, the 2 key correlates for transmission of SARS-CoV-2 within a household are sharing a bedroom and increased viral load, consistent with increased exposure to the infected individual.

Spatial statistical and environmental correlation analyses on vector density, vector infection index and Japanese encephalitis cases at the village and pigsty levels in Liyi County, Shanxi Province, China

BackgroundIn the eco-epidemiological context of Japanese encephalitis (JE), geo-environmental features influence the spatial spread of the vector (Culex tritaeniorhynchus, Giles 1901) density, vector infection, and JE cases.MethodsIn Liyi County, Shanxi Province, China, the spatial autocorrelation of mosquito vector density, vector infection indices, and JE cases were investigated at the pigsty and village scales. The map and Enhanced Thematic Mapper (ETM) remote sensing databases on township JE cases and geo-environmental features were combined in a Geographic Information System (GIS), and the connections among these variables were analyzed with regression and spatial analyses.ResultsAt the pigsty level, the vector density but not the infection index of the vector was spatially autocorrelated. For the pigsty vector density, the cotton field area was positively related, whereas the road length and the distance between pigsties and gullies were negatively related. In addition, the vector infection index was correlated with the pigsty vector density (PVD) and the number of pigs. At the village level, the vector density, vector infection index, and number of JE cases were not spatially autocorrelated. In the study area, the geo-environmental features, vector density, vector infection index, and JE case number comprised the Geo-Environment-Vector-JE (GEVJ) intercorrelation net system. In this system, pig abundance and cotton area were positive factors influencing the vector density first. Second, the infection index was primarily influenced by the vector density. Lastly, the JE case number was determined by the vector infection index and the wheat area.ConclusionsThis study provided quantitative associations among geo-environmental features, vectors, and the incidence of JE in study sties, one typical northern Chinese JE epidemiological area without rice cultivation. The results highlighted the importance of using a diverse range of environmental management methods to control mosquito disease vectors and provided useful information for improving the control of vector mosquitoes and reducing the incidence of JE in the northern Chinese agricultural context.Graphical

Transmissibility of SARS-CoV-2 Variants as a Secondary Attack in Thai Households: a Retrospective Study

ObjectiveSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spreads through person-to-person contact via small droplet particles, especially in poorly ventilated indoor settings such as households, estimating at 16.6% of secondary attack rate. This study aimed to explore the secondary attack rate in Thai households during the new SARS-CoV-2 variant outbreak. MethodsWe obtained a retrospective study of exposed members in households among 30 sets of patients with reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed SARS-CoV-2 infection (index cases) at Chulabhorn Hospital, Bangkok, Thailand, from May 1 to June 30, 2021. Characteristic of index cases and households were extracted from medical records and analyzed. ResultsThe 30 index cases were associated with 157 exposed household close contacts. Seventy-six were RT-PCR confirmed SARS-CoV-2 infections within 14 days after being exposed from an index case, with a secondary attack rate of 48%. However, there was no difference between secondary attack rates among the age of contact, household size, or SARS-CoV-2 variants. ConclusionOur data show high transmissibility of SARS-CoV-2, which was notably exaggerated compared to previous studies. Therefore, developing preventive strategies such as post-exposure prophylaxis (PEP) in close contact with SARS-CoV-2 infection would be a novel supplement to the current standard of care.

An Experience of 436 COVID-19 Patients in Bangladesh

SARS-CoV-2 corona virus infection (COVID-19) is a public health emergency of international concern causing many deaths. The aim of this study was to assess demography, clinical presentation, blood group, disease severity and outcome of COVID-19 infected patients in Bangladesh. This is a cross sectional, observational study of 436 COVID- 19 infected patients, confirmed by RT-PCR assay's on nasopharyngeal swab specimens, presented at Faridpur Medical College Hospital and Kurmitola General Hospital during the month of May to September, 2020. Data were collected in a preformed data sheet and analyzed for variables included demography, source of infection, spreading within family, clinical features, blood group, disease severity and outcome. Study showed mean age 41.27±16.65 years with slight male predominance (1.87:1), most were service holder (47%), source of infection was unknown (40%), from infected family members (35%) and working place (23%). In 44% cases, family members of infected index cases were unaffected. Common co-morbidities were Diabetes Mellitus (19.7%) and Hypertension (19%). Blood group of most (41.29%) was B positive. Disease spectrum ranged from asymptomatic (15%), mild (53%), moderate (19%) and severe (13%) disease. Common presenting symptoms were fever (72.2%), cough (42.9%) dyspnoea (29.6%), myalgia (22.9%), anorexia (17.9%), fatigue (17.4%), diarrhea (13.5%), headache (12.4%) and anosmia (12.4%). Majority (75.2%) had nonspecific (fever, mayalgia, fatigue) symptoms and in 16.28% cases it was the only presentation. Respiratory (61.9%) and GI (28.4%) symptoms presented either concomitantly or with nonspecific symptoms (55%). Majority (95%) of patients recovered and only 5% died. Faridpur Med. Coll. J. Jan 2020;15(2): 53-57

Severe Acute Respiratory Syndrome Coronavirus 2 Transmission in a Georgia School District—United States, December 2020–January 2021

BackgroundTo inform prevention strategies, we assessed the extent of SARS-CoV-2 transmission and settings in which transmission occurred in a Georgia public school district.MethodsDuring December 1, 2020–January 22, 2021, SARS-CoV-2–infected index cases and their close contacts in schools were identified by school and public health officials. For in-school contacts, we assessed symptoms and offered SARS-CoV-2 RT-PCR testing; performed epidemiologic investigations and whole-genome sequencing to identify in-school transmission; and calculated secondary attack rate (SAR) by school setting (e.g., sports, elementary school classroom), index case role (i.e., staff, student), and index case symptomatic status.ResultsWe identified 86 index cases and 1,119 contacts, 688 (63.1%) of whom received testing. Fifty-nine (8.7%) of 679 contacts tested positive; 15 (17.4%) of 86 index cases resulted in ≥2 positive contacts. Among 55 persons testing positive with available symptom data, 31 (56.4%) were asymptomatic. Highest SAR were in indoor, high-contact sports settings (23.8%, 95% confidence interval [CI] 12.7, 33.3), staff meetings/lunches (18.2%, CI 4.5–31.8), and elementary school classrooms (9.5%, CI 6.5–12.5). SAR was higher for staff (13.1%, CI 9.0–17.2) versus student index cases (5.8%, CI 3.6–8.0) and for symptomatic (10.9%, CI 8.1–13.9) versus asymptomatic index cases (3.0%, CI 1.0–5.5).ConclusionsIndoor sports may pose a risk to the safe operation of in-person learning. Preventing infection in staff members, through measures that include COVID-19 vaccination, is critical to reducing in-school transmission. Because many positive contacts were asymptomatic, contact tracing should be paired with testing, regardless of symptoms.

Em época de Pandemia: Covid-19 como Doença Profissional- a experiência de um Instituto Português de Oncologia

INTRODUCTION The novel coronavirus, called SARS-CoV-2, has as its main factor of the disease spreading the transmission between humans. COVID-19 is the name given by the World Health Organization (WHO) to identify the disease caused by this agent. Portugal is currently experiencing the pandemic Mitigation phase, in which, in addition to community transmission, it is assumed that there is local transmission in a closed environment. This disease was recognized by the WHO and by the Portugal Directorate-General of Health as Occupational Disease in a health care environment. OBJECTIVE Evaluate and characterize the presumed cases of occupational disease caused by SARS-CoV-2, among workers with COVID-19, considering the respective interpretation of the causal nexus, individually. METHODS Retrospective, descriptive, observational study (case-series), carried out between march and july 2020 in workers of a Portuguese oncology institute, dedicated to provide care for patients with cancer, reviewing files in the clinical processes of the occupational health service software (UTILSST®). It was considered the infection of workers with SARS-COV-2, as an inclusion criterion. RESULTS 41 workers were diagnosed with COVID-19, with an average age of 43.70 ± 11.63 years. Of these, 87.80% (n= 36) were female. The professional category with the highest infection rate in the institution was the auxiliaries of nursing [46.34%, n= 19], followed by nurses [39.02%, n = 16]. The most affected service was a Medical Oncology Service [31.4%, n= 11]. In the studied population, the prevalence of cases presumed to be Occupational Disease was 80.49% (n= 33). Of these, 48.5% (n= 16) were by direct contact with an infected patient, 30.3% (n = 10) without a known index case, but with a diagnosis obtained in “Disease mitigation phase” and 21.2% (n=7) by contact with an infected worker. In 19.51% (n= 8) of all the cases, no Occupational Disease was presumed, due to contact with an infected index case in a social/ family environment. CONCLUSION The main sources of nosocomial transmission with an assumed causal nexus are patients with COVID-19. It is essential to put into practice and ensure the maintenance of adequate collective and individual protection measures to combat this disease, as well as ensuring a permanent update of the institution’s infection control program so that the risk of exposure is controlled.

Survey on neutralizing antibodies against Zika virus eighteen months post-outbreak in two southern Thailand communities

BackgroundIn 2016 and 2017, Zika virus (ZIKV) infection outbreaks occurred in two communities in southern Thailand. This re-immerging infection can widely spread by mosquito bites and cause serious complications in a central nervous system among children born to infected mothers. Thus, they should be protected. This study aims to (1) To determine the prevalence of neutralizing ZIKV antibodies in the post-outbreak areas among the general population and pregnancy women residing at various distances from the houses of the nearest index patients; (2) To examine the cross-neutralizing capacity of antibodies against ZIKV on other flaviviruses commonly found in the study areas; (3) To identify factors associated with the presence of neutralizing ZIKV antibodies.MethodsThe two post-outbreak communities were visited at 18 months after the outbreaks. We enrolled (1) 18 confirmed ZIKV infected (index) cases, (2) sample of 554 neighbors in the outbreak areas who lived at various distances from the index patients’ houses, (3) 190 residents of non-outbreak areas, and (4) all pregnant women regardless of gestational age residing in the study areas (n = 805). All serum specimens underwent the plaque reduction neutralization test (PRNT). Ten randomly selected ZIKV seropositive and ten randomly selected seronegative specimens were tested for dengue virus serotypes 1–4 (DENV1–4) and Japanese encephalitis virus (JEV) antibodies using PRNT90. Serum titer above 1:10 was considered positive. Multiple logistic regression was used to assess factors associated with seropositivity.ResultsOut of all 18 index cases, 9 remained seropositive. The seroprevalence (95% CI) in the two outbreak areas were 43.7% (35.9–51.6%) and 29.7% (23.3–36.0%) in general population, and 24.3% (20.1–28.8%) and 12.8% (9.7–16.5%) in pregnant women. Multivariate analysis showed that seropositivity was independent of the distance gradient from the index’s houses. However, being elderly was associated with seropositivity. DENV1–4 and JEV neutralizing antibodies were present in most ZIKV-positive and negative subsamples.ConclusionProtective herd immunity for ZIKV infection is inadequate, especially among pregnant women in the two post-outbreak areas in southern Thailand.

Extended screening of Trypanosoma cruzi among the offspring of infected women. Barcelona North metropolitan area, Catalonia (Spain), 2005–2016

IntroductionTo date, very little data is available on the extensive, familiar, serological screening of Trypanosoma cruzi from infected-index cases. As it is a parasite with possibility of mother-to-child foetal transmission, the study of the offspring of chronically infected women has a special relevance. MethodsAn observational study using a capture-recapture method that evaluates the offspring serological status of women diagnosed with T. cruzi infection (positive serology) in the northern metropolitan area of Barcelona during 2005–2016. ResultsA total of 238 women with positive serology for T. cruzi were identified. Of these, 117 (49.2%) could be localised. Their offspring summarised 300 individuals, of which 192 (64%) had serology records, with 23 positive for T. cruzi (11.98%; CI95%: 8.1–17.3). Among the 53 children born within the study area, 5 (9.8%, CI95%: 4.2–20.9) cases of vertical transmission were recorded. All children born as of 2010 (the starting year of mother screening) had serological outputs. ConclusionsOffspring of T. cruzi-seropositive women showed a high rate of seropositivity. The prevalence of vertical transmission is also remarkably high but comparable to that obtained in other European studies. The main source of loss was non-accessible women. It is reasonable to formally include extensive, familiar, serological assessment in Chagas screening guidelines. In order to avoid losses, any eventual screening should be implemented at the time of the maternal diagnosis.

Assessment of the Isoniazid Preventive Therapy Uptake and Associated Characteristics: A Cross-Sectional Study.

Objective To assess the uptake of isoniazid preventive therapy (IPT) by eligible children in Kigali, Rwanda, and associated individual, households, and healthcare systems characteristics. Methods A cross-sectional study was conducted among child contacts of index cases having sputum smear-positive pulmonary tuberculosis. Data were collected from 13 selected primary health centres. Descriptive statistics were used to generate frequency tables and figures. Logistic regression models were performed to determine characteristics associated with IPT uptake. Results Of 270 children (under 15 years), who were household contacts of 136 index cases, 94 (35%) children were less than 5 years old and eligible for IPT; and 84 (89%, 95% CI 81–94) were initiated on IPT. The reasons for not initiating IPT in the remaining 10 children were parents/caregivers' lack of information on the need for IPT, refusal to give IPT to their children, and poor quality services offered at health centres. Factors associated with no uptake of IPT included children older than 3 years, unfriendly healthcare providers, HIV infected index cases, and the index case not being the child's parent. Conclusion The National Tuberculosis Program's policy on IPT delivery was effectively implemented. Future interventions should find strategies to manage factors associated with IPT uptake.

Cribado ampliado de Trypanosoma cruzi en la descendencia de mujeres infectadas en la zona metropolitana norte de Barcelona, Cataluña (España), 2005-2016

IntroductionTo date, very little data is available on the extensive, familiar, serological screening of Trypanosoma cruzi from infected-index cases. As it is a parasite with possibility of mother-to-child fetal transmission, the study of the offspring of chronically infected women has a special relevance. MethodsAn observational study using a capture-recapture method that evaluates the offspring serological status of women diagnosed with T. cruzi infection (positive serology) in the northern metropolitan area of Barcelona during 2005-2016. ResultsA total of 238 women with positive serology for T. cruzi were identified. Of these, 117 (49.2%) could be localized. Their offspring summarized 300 individuals, of which 192 (64%) had serology records, with 23 positive for T. cruzi (11.98%; CI95%: 8.1-17.3). Among the 53 children born within the study area, 5 (9.8%, CI95%: 4.2-20.9) cases of vertical transmission were recorded. All children born as of 2010 (the starting year of mother screening) had serological outputs. ConclusionsOffspring of T. cruzi-seropositive women showed a high rate of seropositivity. The prevalence of vertical transmission is also remarkably high but comparable to that obtained in other European studies. The main source of loss was non-accessible women. It is reasonable to formaly include extensive, familiar, serological assessment in Chagas screening guidelines. In order to avoid losses, any eventual screening should be implemented at the time of the maternal diagnosis.

Silent dissemination of HTLV-1 in an endemic area of Argentina. Epidemiological and molecular evidence of intrafamilial transmission.

BackgroundMolecular and epidemiological studies of transmission routes and risk factors for infection by HTLV-1 are extremely important in order to implement control measures, especially because of the high prevalence of HTLV-1 in several regions of the world. San Salvador de Jujuy, Northwest Argentina, is a highly endemic area for HTLV-1 and foci of tropical spastic paraparesis/HTLV-1-associated myelopathy.ObjectiveTo gain further insight into the role of intrafamilial transmission of HTLV-1 in a highly endemic region in Argentina.MethodCross-sectional study in Northwest Argentina. Epidemiological data and blood samples were collected from 28 HTLV-1 infected subjects (index cases) and 92 close relatives/cohabitants. HTLV-1 infection was diagnosed by detection of antibodies and proviral DNA. The LTR region was sequenced and analyzed for genetic distances (VESPA software), in addition to determination and identification of polymorphisms to define HTLV-1 family signatures.ResultsFifty seven of the 120 subjects enrolled had antibodies against HTLV-1 and were typified as HTLV-1 by PCR. The prevalence rate of HTLV-1 infection in family members of infected index cases was 31.52% (29/92). The infection was significantly associated with gender, age and prolonged lactation. Identity of LTR sequences and presence of polymorphisms revealed high prevalence of mother-to-child and interspousal transmission of HTLV-1 among these families.ConclusionThere is an ongoing and silent transmission of HTLV-1 through vertical and sexual routes within family clusters in Northwest Argentina. This evidence highlights that HTLV-1 infection should be considered as a matter of public health in Argentina, in order to introduce preventive measures as prenatal screening and breastfeeding control.

Historical outbreak of Salmonella hadar

This article reports a historical outbreak of Salmonella hadar in a maternity setting. The outbreak occurred following admission of an infected index case, with transmission to 11 other individuals over a three-month period in a maternity and neonatal unit. Despite rigorous assessment of clinical practices, screening of patients and staff, and review of disinfection and sterilization policies, the outbreak was difficult to control. This possibly reflects the capacity of S.hadar to survive well in the environment, and cause prolonged and asymptomatic carriage with intermittent shedding. It is likely that the index case was a mother who had contracted infection after eating suspect food. Additionally, infection may have been perpetuated by shared use of tubes of yellow soft paraffin for lubrication of digital rectal thermometers. This outbreak emphasizes the difficulties in controlling outbreaks of S.hadar infection in an obstetric/neonatal setting, and also emphasizes the importance of early stool sampling in any patient with diarrhoeal symptoms.

Estimating the Reproduction Number of Ebola Virus (EBOV) During the 2014 Outbreak in West Africa.

The 2014 Ebola virus (EBOV) outbreak in West Africa is the largest outbreak of the genus Ebolavirus to date. To better understand the spread of infection in the affected countries, it is crucial to know the number of secondary cases generated by an infected index case in the absence and presence of control measures, i.e., the basic and effective reproduction number. In this study, I describe the EBOV epidemic using an SEIR (susceptible-exposed-infectious-recovered) model and fit the model to the most recent reported data of infected cases and deaths in Guinea, Sierra Leone and Liberia. The maximum likelihood estimates of the basic reproduction number are 1.51 (95% confidence interval [CI]: 1.50-1.52) for Guinea, 2.53 (95% CI: 2.41-2.67) for Sierra Leone and 1.59 (95% CI: 1.57-1.60) for Liberia. The model indicates that in Guinea and Sierra Leone the effective reproduction number might have dropped to around unity by the end of May and July 2014, respectively. In Liberia, however, the model estimates no decline in the effective reproduction number by end-August 2014. This suggests that control efforts in Liberia need to be improved substantially in order to stop the current outbreak.

Optimal design of studies of influenza transmission in households. II: Comparison between cohort and case-ascertained studies

Both case-ascertained household studies, in which households are recruited after an 'index case' is identified, and household cohort studies, where a household is enrolled before the start of the epidemic, may be used to test and estimate the protective effect of interventions used to prevent influenza transmission. A simulation approach parameterized with empirical data from household studies was used to evaluate and compare the statistical power of four study designs: a cohort study with routine virological testing of household contacts of infected index case, a cohort study where only household contacts with acute respiratory illness (ARI) are sampled for virological testing, a case-ascertained study with routine virological testing of household contacts, and a case-ascertained study where only household contacts with ARI are sampled for virological testing. We found that a case-ascertained study with ARI-triggered testing would be the most powerful design while a cohort design only testing household contacts with ARI was the least powerful. Sensitivity analysis demonstrated that these conclusions varied by model parameters including the serial interval and the risk of influenza virus infection from outside the household.

Case and partnership reproduction numbers for a curable sexually transmitted infection

Sexually transmitted infections (STIs) are, by definition, transmitted between sexual partners. For curable STIs an infected index case can potentially re-infect the same partner multiple times. Thus, R0, the average number of secondary infections one typical infected individual will produce during his or her infectious period is not necessarily the same as the average number of secondary cases (infected persons). Here we introduce the new concept of the case reproduction number (Rc). In addition, we define the partnership reproduction number (Rp) as the average number of secondary partnerships consisting of two infected individuals one typical infected individual will produce over his or her infectious lifetime. Rp takes into account clearance and re-infection within partnerships, which results in a prolongation of the duration of the infectious period. The two new reproduction numbers were derived for a deterministic pair model with serial monogamous partnerships using infection parameters for Chlamydia trachomatis, an example of a curable STI. We showed that re-infection within partnerships means that curable STIs can be sustained endemically even when the average number of secondary cases a person produces during his or her infectious period is below one.

Intrafamilial seropositivity of hepatitis in patients with hepatitis B and C virus in hepatitis clinic in Hamadan, Iran

Objective. To determine intrafamilial seropositivity of HBV and HCV and to compare them in families of infected persons with HBV and HCV in Hamadan clinic of hepatitis.Material and methods. In this analytic cross-sectional study, 651 family members of 200 HBV and HCV infection index cases were entered into the study and after signing an informed consent, they were referred to Blood Transfusion Center. With completion of laboratory tests, interviewers filled the questionnaires.Results. One hundred and eighteen (20.5%) and 107 (18.6%) family members were HBsAg and HBcAb positive respectively. 21 (3.6%) were isolated HBcAb positive. Only one person (1.3%) was HCVAb positive. The general rate of infection in family members of HBV infected people (atleast one case) (49.4%) was significantly higher than that of HCV infected people (3.3%), p < 0.001. Interspouses transmission was evaluated and prevalence of interspouses HBV and HCV infection were 32.3 and 8%, respectively.Conclusion. Intrafamilial and interspousal seropositivity of HBV is obviously more than those of HCV. More attention should be paid to screening and risk lowering activities particularly about HBV infected people and their families.

Mantoux skin test reactivity among household contacts of hiv-infected and hiv un-infected patients with sputum smear positive TB in Dar Es Salaam, Tanzania

To compare the prevalence of Tuberculosis (TB) infection as demonstrated by a positive Mantoux skin test (MST) among household contacts of sputum smear positive (SSP) HIV infected and un-infected TB patients. A cross-sectional study of household contacts of patients with TB (index cases) attending Muhimbili National Hospital, and TB clinics of Infectious Disease Control Centre and Municipal hospitals in Dar es Salaam. Index cases with SSP-TB and aged > or =18 years had their HIV serostatus determined by ELISA. Contacts of index cases aged > or =1 year received intradermal protein-purified derivative (Mantoux test) and results were read after 72 hours. Infected contacts (MST-positive) received medical evaluation to exclude TB disease. The overall prevalence of TB infection among contacts of HIV infected and un-infected index cases were 61.6% and 62.5% respectively, (OR 1.04 [95% CI 0.61-1.76], p=0.887). Factors associated with an increased risk of TB infection among contacts of both HIV infected and un-infected index cases were: older age of contacts (> or =25 years), duration of living with index case prior to TB diagnosis of > or =1 year, and sharing a room with index case. Infectiousness to their contacts was higher among female compared to male index cases. The proportion of household contacts of SSP PTB index cases with a positive MST was high and uninfluenced by the HIV serostatus of the index case. Efforts towards contact tracing and screening for TB among close contacts of SSP PTB patients should be enhanced.

Human T Lymphotropic Virus Type 1 Subtype C Melanesian Genetic Variants of the Vanuatu Archipelago and Solomon Islands Share a Common Ancestor

Melanesia is endemic for human T lymphotropic virus type 1 (HTLV-1) subtype C. In 2005, we identified 4 infected women from Ambae Island, Vanuatu. Subsequently, 4247 Ni-Vanuatu originating from 18 islands were enrolled to define HTLV-1 epidemiological determinants and to characterize the viral strains molecularly. Plasma from 1074 males and 3173 females were screened for HTLV-1/2 antibodies by particle agglutination (PA) and an immunofluorescence assay (IFA). Positive and/or borderline samples were then tested by a Western blot (WB) confirmatory assay. DNAs were amplified to obtain a 522-bp env gene fragment. Phylogenetic and molecular-clock analyses were performed. Of 4247 samples, 762 were positive and/or borderline by IFA/PA, and 26 of them were confirmed to be HTLV-1 positive by WB. The overall HTLV-1 seroprevalence was 0.62%. Viral transmission was found within families of infected index case patients. A geographic heterogeneity of HTLV-1 seroprevalence was observed among the islands. All 41 of the new env sequences belonged to HTLV-1 subtype C. Phylogenetic and molecular-clock analyses suggested that Ni-Vanuatu and Solomon Islander strains emerged from a common ancestor ~10,000 years ago. The Vanuatu archipelago is endemic for HTLV-1 with a diversity of subtype C variants. These strains were probably introduced into Vanuatu during ancient migration of the original settlers a few thousand years ago.

High Prevalence of Congenital Trypanosoma cruzi Infection and Family Clustering in Salta, Argentina

Trypanosoma cruzi, the causative agent of Chagas' disease, is transmitted mainly by insect vectors, but congenital and transfusion-borne infections occasionally occur. The factors that are involved in transmission from mother to offspring are not well understood. The objective of this study was to study the presence of T cruzi infection in children who were born to infected mothers and in the children's siblings to evaluate the epidemiologic risk factors associated with congenital transmission of Chagas' disease. Congenital T cruzi infection was studied in 340 children who were born to chronically infected mothers in Salta, Argentina. Infection was detected in 31 children, who were selected for additional study as infected index cases (IIC). Of the 309 noninfected children, 31 were taken as noninfected index cases (NIIC). We compared the prevalence of congenital T cruzi transmission in the remaining siblings of the IIC and NIIC. Data and blood samples were collected in house-to-house visits. Diagnosis of infection was established mainly by serologic methods, indirect hemmagglutination, and enzyme-linked immunosorbent assay. The prevalence was 31.4% (32 of 102 children) for IIC siblings, whereas no infected siblings were found in families with NIIC (0 of 112). Clustering of congenital infection was found in 14 families, in which >1 child was infected. Second-generation congenital transmission (from grandmother to mother to newborn) was established in 4 families. The association among low weight at birth, prematurity, and congenital transmission was highly significant. An important observation was the absence of pathologic findings in a high proportion of infected children. The detection of asymptomatic infections was a consequence of population screening, as opposed to hospital-based diagnosis, for which symptomatic cases predominate. Congenital transmission was associated with the geographic origin of mothers: women from areas where insect vectors proliferate were less likely to give birth to infected offspring than women from areas under active vector control. Siblings of an infant infected with T cruzi are at high risk for infection themselves and, even in the absence of symptoms, should also be screened for infection. The findings of family clustering of infection and of second-generation congenital infection in vector-free areas suggest that new modalities of transmission, other than classic vector-borne spread, may occur both in endemic and in nonendemic areas.