Epidemiology and transmission of COVID-19 in cases and close contacts in Georgia in the first four months of the epidemic

AbstractBackgroundBetween February and June 2020, 917 COVID-19 cases and 14 COVID-19-related deaths were reported in Georgia. Early on, Georgia implemented non-pharmaceutical interventions (NPI) including extensive contact tracing and restrictions on movement.AimTo characterize the demographics of those tested and infected with COVID-19 in Georgia; to evaluate factors associated with transmission between cases and their contacts; and to determine how transmission varied due to NPI up to 24 June 2020.MethodsWe use data gathered by the Georgian National Center for Disease Control on all polymerase chain reaction tests conducted (among symptomatic patients, through routine testing and contact tracing); hospitalization data for confirmed cases, and contact tracing data. We calculated the number of contacts per index case, the secondary attack rate (% contacts infected), and effective R number (new cases per index case), and used logistic regression to estimate how age, gender, and contact type affected transmission.ResultsMost contacts and transmission events were between family members. Contacts <40 years were less likely to be infected, while infected individuals >50 were more likely to die than younger patients. Contact tracing identified 917 index cases with mean 3.1 contacts tested per case, primarily family members. The overall secondary attack rate was 28% (95% confidence interval [CI]: 26-29%) and effective R number was 0.87 (95%CI 0.81-0.93), peaking at 1.1 (95%CI 0.98-1.2) during the period with strongest restrictions.ConclusionGeorgia effectively controlled the COVID-19 epidemic in its early stages, although evidence does not suggest transmission was reduced during the strict lockdown period.Research in ContextEvidence before this studyWe searched PubMed and MedRxiv for papers reporting research using contact tracing data to evaluate the characteristics of the COVID-19 epidemic in any country. A number of analyses were identified from Asia, including China, Taiwan, Maldives, Thailand, South Korea, and India, but none from other regions other than one previous analysis conducted in Europe, focusing on the first two months of the COVID-19 epidemic in Cyprus. Studies evaluated number of contacts and different contact types, secondary attack rate, and effective R number. However, none of these studies compared characteristics between different time periods or under varied levels of non-pharmaceutical interventions or restrictions on social mixing.Added value of this studyIn this study, we use contact tracing data from Georgia from all cases identified in the first four months of the epidemic, as well as testing and hospitalization data, to evaluate the number and type of contacts, effective R number (new cases per index case), and secondary attack rate (proportion of contacts infected) in this population, and whether these measures changed before, during, and after the lockdown period. We also evaluated how the chance of transmission varied by type of index case and contact. Our results indicate that number of contacts remained relatively low throughout the study period, so although the secondary attack rate was relatively high (28%) compared to that seen in studies in Asia (10-15%), the effective R number was less than one overall, peaking at 1.1 (0.98-1.2) during the strictest lockdown period, with easing of restrictions corresponding to a lower effective R of 0.87 (0.77-0.97). Most transmission occurred between family members with transmission very low between co-workers, friends, neighbours, and medical personnel, indicating that the restrictions on social mixing were effective at keeping the epidemic under control during this period.Implications of all the available evidenceOur study presents the first analysis of the successful control of a COVID-19 epidemic in a European country, indicating that despite a high secondary attack rate, reduction in contacts outside the home, and a well-timed lockdown, were able to keep transmission under control.

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Role of children in household transmission of COVID-19

Archives of Disease in Childhood ◽

10.1136/archdischild-2020-319910 ◽

2020 ◽

pp. archdischild-2020-319910 ◽

Cited By ~ 13

Author(s):

Jieun Kim ◽

Young June Choe ◽

Jin Lee ◽

Young Joon Park ◽

Ok Park ◽

...

Keyword(s):

Attack Rate ◽

Index Case ◽

Clinical Findings ◽

International Travel ◽

Contact Tracing ◽

Secondary Case ◽

Household Transmission ◽

Household Members ◽

Index Cases

ObjectiveTransmissibility of COVID-19 by children in the household is not clear. Herein, we describe children’s role in household transmission of COVID-19.Design and settingAll paediatric COVID-19 index cases and their household members reported from 20 January to 6 April 2020 in South Korea were reviewed. The secondary attack rate (SAR) from child index case to household secondary case was calculated. Epidemiological and clinical findings of child index case-household secondary case pair was assessed.ResultsA total of 107 paediatric COVID-19 index cases and 248 of their household members were identified. One pair of paediatric index-secondary household case was identified, giving a household SAR of 0.5% (95% CI 0.0% to 2.6%). The index case was self-quarantined at home after international travel, stayed in her room, but shared a meal table with the secondary case.ConclusionThe SAR from children to household members was low in the setting of social distancing, underscoring the importance of rigorous contact tracing and early isolation in limiting transmission within households.

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Estimation of the Secondary Attack Rate for Delta Hepatitis Coinfection among Injection Drug Users

Canadian Journal of Infectious Diseases ◽

10.1155/1993/539613 ◽

1993 ◽

Vol 4 (1) ◽

pp. 47-51 ◽

Cited By ~ 2

Author(s):

Christiane Poulin ◽

Theresa Gyorkos ◽

Lawrence Joseph

Keyword(s):

Nova Scotia ◽

Hepatitis B ◽

Confidence Interval ◽

Rural Area ◽

Attack Rate ◽

Injection Drug Users ◽

Drug Users ◽

Index Case ◽

Injection Drug ◽

Contact Tracing

The secondary attack rate for delta hepatitis coinfection was estimated among a cluster of injection drug users (IDUs). The infections occurred during an epidemic of hepatitis B in a rural area of Nova Scotia in 1988 and 1989. Six IDUs formed a cluster of delta hepatitis coinfections, representing the first reported outbreak of delta hepatitis in Canada. Contact-tracing was used to identify a cluster of 41 IDUs potentially exposed to delta hepatitis. The index case of delta hepatitis coinfection was presumed to have led to five secondary cases. The secondary attack rate was estimated to be 13.2% (95% confidence interval 0.044 to 0.281). The estimated secondary attack rate may be a useful predictor of disease due to delta hepatitis coinfection in similar IDU populations.

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Secondary transmission of SARS-CoV-2 in educational settings in Northern Italy from September 2020 to April 2021: a population-based study

10.1101/2021.09.03.21263061 ◽

2021 ◽

Author(s):

Olivera Djuric ◽

Elisabetta Larosa ◽

Mariateresa Cassinadri ◽

Silvia Cilloni ◽

Eufemia Bisaccia ◽

...

Keyword(s):

Attack Rate ◽

Index Case ◽

School Setting ◽

Population Based ◽

Contact Tracing ◽

Secondary Case ◽

Secondary Transmission ◽

Source Of Infection ◽

Alpha Variant ◽

Type Of School

Background: We aimed to quantify the risk of transmission of SARS-CoV-2 in the school setting by type of school, characteristics of the index case and calendar period in the Reggio Emilia province (RE), Italy, from school reopening in September 2020 until the beginning of April 2021. The secondary aim was to estimate the promptness of contact tracing. Methods: A population-based analysis of surveillance data of all COVID-19 cases occurring in RE, Italy, from September 1, 2020, to April 4th, 2021, for which a school contact and/or exposure was suspected. Indicator of the delay in contact tracing was computed as the time elapsed since positivity of the index case and the date on which the swab for classmates was scheduled (or most were scheduled). Results: Overall, 30,426 and 13,571 contacts among classmates and teachers/staff, respectively, were identified and received recommendation for testing; 43,414 (98.7%) performed the test. Secondary transmission occurred in about 40% of the investigated classes, and the overall secondary case attack rate was 4%, slightly higher when the index case was a teacher, but with almost no differences by type of school and stable during the study period. Promptness of contact tracing increased during the study period, reducing the time from index case identification and testing of contacts from 7 to 3 days, as well the ability to identify possible source of infection in the index case (from 42% in September/October, to 22% in November, to 50% in December-April). Conclusions: Despite the spread of the Alpha variant during the study period in RE, the secondary case attack rate remained stable from school reopening in September 2020 until the beginning of April 2021.

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Using Non-Pharmaceutical Interventions and High Isolation of Asymptomatic Carriers to Contain the Spread of SARS-CoV-2 in Nursing Homes

10.1101/2021.01.22.21249308 ◽

2021 ◽

Author(s):

Alec J. Schmidt ◽

Yury García ◽

Diego Pinheiro ◽

Tom Reichert ◽

Miriam A. Nuño

Keyword(s):

Attack Rate ◽

Group Living ◽

Daily Basis ◽

Contact Tracing ◽

Term Care ◽

Care Facilities ◽

Degree Of Control ◽

Antigen Tests ◽

Pharmaceutical Interventions

ABSTRACTObjectiveUsing a pandemic influenza model modified for COVID-19, this study investigated the degree of control over pre-symptomatic transmission that common non-pharmaceutical interventions (NPIs) would require to reduce the spread in long-term care facilities.MethodsWe created a stochastic compartmental SEIR model with Poisson-distributed transition states that compared the effect of R0, common NPIs, and isolation rates of pre-symptomatic carriers primarily on attack rate, peak cases, and timing in a 200-resident nursing home. Model sensitivity was assessed with 1st order Sobol’ indices.ResultsThe most rigorous NPIs decreased the peak number of infections by 4.3 and delayed the peak by 9.7 days in the absence of pre-symptomatic controls. Reductions in attack rate were not likely, even with rigorous application of all defined NPIs, unless pre-symptomatic carriers were identified and isolated at rates exceeding 76%. Attack rate was most sensitive to the pre-symptomatic isolation rate (Sobol’ index > 0.7) and secondarily to R0.ConclusionsCommon NPIs delayed and reduced epidemic peaks. Reducing attack rates ultimately required efficient isolation of pre-symptomatic cases, including rapid antigen tests on a nearly daily basis. This must be accounted for in testing and contact tracing plans for group living settings.

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A sub-national analysis of the rate of transmission of COVID-19 in Italy

10.1101/2020.05.05.20089359 ◽

2020 ◽

Cited By ~ 1

Author(s):

Michaela A. C. Vollmer ◽

Swapnil Mishra ◽

H Juliette T Unwin ◽

Axel Gandy ◽

Thomas A Mellan ◽

...

Keyword(s):

Attack Rate ◽

Herd Immunity ◽

Transmission Intensity ◽

Contact Tracing ◽

Social Distancing ◽

Italian Regions ◽

Transmission Reduction ◽

Using Data ◽

National Analysis ◽

Pharmaceutical Interventions

Italy was the first European country to experience sustained local transmission of COVID-19. As of 1st May 2020, the Italian health authorities reported 28,238 deaths nationally. To control the epidemic, the Italian government implemented a suite of non-pharmaceutical interventions (NPIs), including school and university closures, social distancing and full lockdown involving banning of public gatherings and non essential movement. In this report, we model the effect of NPIs on transmission using data on average mobility. We estimate that the average reproduction number (a measure of transmission intensity) is currently below one for all Italian regions, and significantly so for the majority of the regions. Despite the large number of deaths, the proportion of population that has been infected by SARS-CoV-2 (the attack rate) is far from the herd immunity threshold in all Italian regions, with the highest attack rate observed in Lombardy (13.18% [10.66%-16.70%]). Italy is set to relax the currently implemented NPIs from 4th May 2020. Given the control achieved by NPIs, we consider three scenarios for the next 8 weeks: a scenario in which mobility remains the same as during the lockdown, a scenario in which mobility returns to pre-lockdown levels by 20%, and a scenario in which mobility returns to pre-lockdown levels by 40%. The scenarios explored assume that mobility is scaled evenly across all dimensions, that behaviour stays the same as before NPIs were implemented, that no pharmaceutical interventions are introduced, and it does not include transmission reduction from contact tracing, testing and the isolation of confirmed or suspected cases. New interventions, such as enhanced testing and contact tracing are going to be introduced and will likely contribute to reductions in transmission; therefore our estimates should be viewed as pessimistic projections. We find that, in the absence of additional interventions, even a 20% return to pre-lockdown mobility could lead to a resurgence in the number of deaths far greater than experienced in the current wave in several regions. Future increases in the number of deaths will lag behind the increase in transmission intensity and so a second wave will not be immediately apparent from just monitoring of the daily number of deaths. Our results suggest that SARS-CoV-2 transmission as well as mobility should be closely monitored in the next weeks and months. To compensate for the increase in mobility that will occur due to the relaxation of the currently implemented NPIs, adherence to the recommended social distancing measures alongside enhanced community surveillance including swab testing, contact tracing and the early isolation of infections are of paramount importance to reduce the risk of resurgence in transmission.

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Cluster of COVID-19 in northern France: A retrospective closed cohort study

10.1101/2020.04.18.20071134 ◽

2020 ◽

Cited By ~ 41

Author(s):

Arnaud Fontanet ◽

Laura Tondeur ◽

Yoann Madec ◽

Rebecca Grant ◽

Camille Besombes ◽

...

Keyword(s):

High School ◽

Cohort Study ◽

Attack Rate ◽

Herd Immunity ◽

High Sensitivity ◽

Added Value ◽

Contact Tracing ◽

Antibody Detection ◽

Teaching Staff ◽

Predictive Values

SummaryBackgroundThe Oise department in France has been heavily affected by COVID-19 in early 2020.MethodsBetween 30 March and 4 April 2020, we conducted a retrospective closed cohort study among pupils, their parents and siblings, as well as teachers and non-teaching staff of a high-school located in Oise. Participants completed a questionnaire that covered history of fever and/or respiratory symptoms since 13 January 2020 and had blood tested for the presence of anti-SARS-CoV-2 antibodies. The infection attack rate (IAR) was defined as the proportion of participants with confirmed SARS-CoV-2 infection based on antibody detection. Blood samples from two blood donor centres collected between 23 and 27 March 2020 in the Oise department were also tested for presence of anti-SARS-CoV-2 antibodies.FindingsOf the 661 participants (median age: 37 years), 171 participants had anti-SARS-CoV-2 antibodies. The overall IAR was 25.9% (95% confidence interval (CI) = 22.6-29.4), and the infection fatality rate was 0% (one-sided 97.5% CI = 0 - 2.1). Nine of the ten participants hospitalised since mid-January were in the infected group, giving a hospitalisation rate of 5.3% (95% CI = 2.4 –9.8). Anosmia and ageusia had high positive predictive values for SARS-CoV-2 infection (84.7% and 88.1%, respectively). Smokers had a lower IAR compared to non-smokers (7.2% versus 28.0%, P <0.001). The proportion of infected individuals who had no symptoms during the study period was 17.0% (95% CI = – 23.4). The proportion of donors with anti-SARS-CoV-2 antibodies in two nearby blood banks of the Oise department was 3.0% (95% CI = 1.1 - 6.4).InterpretationThe relatively low IAR observed in an area where SARS-CoV-2 actively circulated weeks before confinement measures indicates that establishing herd immunity will take time, and that lifting these measures in France will be long and complex.FundingInstitut Pasteur, CNRS, Université de Paris, Santé publique France, Labex IBEID (ANR-10-LABX-62-IBEID), REACTing, EU grant Recover, INCEPTION project (PIA/ANR-16-CONV-0005).Research in contextEvidence before the studyThe first COVID-19 cases in France were reported on 24 January 2020. Substantial transmission has occurred since then, with the Oise department, north of Paris, one of the heaviest affected areas in the early stages of the epidemic in France. As of 13 April 2020, 98,076 cases had been diagnosed in France, including 5,379 deaths.Epidemiological and clinical characteristics of patients with COVID-19 have been widely reported, but this has largely been centred on cases requiring medical care. What remains unclear at this stage is the extent to which SARS-CoV-2 infections may be asymptomatic or present as subclinical, non-specific symptoms. While extensive contact tracing has identified asymptomatic infections using RT-PCR testing, serologic detection of anti-SARS-CoV-2 antibodies is needed to determine the real infection attack rate and the proportion of all infections that are asymptomatic or subclinical.Added value of this studyUsing a combination of serologic assays with high sensitivity and specificity for anti-SARS-CoV-2 antibodies, we conducted a retrospective closed cohort study. In a high school linked to a cluster of COVID-19 in the Oise department, we showed an overall infection attack rate (IAR) of 40.9% in the high school group, and 10.9% in parents and siblings of the pupils. The proportion of infected individuals who had no symptoms during the study period was 17.0%.Implications of all of the available evidenceThe relatively low IAR in this area where SARS-CoV-2 actively circulated before confinement measures were introduced indicates that establishing herd immunity will take time, and that the lifting of these measures in France will be long and complex.

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Tuberculosis contact investigation results among paediatric contacts in low-incidence settings in Finland

European Journal of Pediatrics ◽

10.1007/s00431-021-04000-7 ◽

2021 ◽

Author(s):

Antti Kontturi ◽

Satu Kekomäki ◽

Eeva Ruotsalainen ◽

Eeva Salo

Keyword(s):

Early Diagnosis ◽

Young Children ◽

Large Scale ◽

Index Case ◽

Contact Tracing ◽

Sputum Smear ◽

Endemic Country ◽

Household Contacts ◽

Contact Investigation ◽

Positive Index

AbstractTuberculosis (TB) risk is highest immediately after primary infection, and young children are vulnerable to rapid and severe TB disease. Contact tracing should identify infected children rapidly and simultaneously target resources effectively. We conducted a retrospective review of the paediatric TB contact tracing results in the Hospital District of Helsinki and Uusimaa from 2012 to 2016 and identified risk factors for TB disease or infection. Altogether, 121 index cases had 526 paediatric contacts of whom 34 were diagnosed with TB disease or infection. The maximum delay until first contact investigation visit among the household contacts under 5 years of age with either TB disease or infection was 7 days. The yield for TB disease or infection was 4.6% and 12.8% for household contacts, 0.5% and 0% for contacts exposed in a congregate setting and 1.4% and 5.0% for other contacts, respectively. Contacts born in a TB endemic country (aOR 3.07, 95% CI 1.10–8.57), with household exposure (aOR 2.96, 95% CI 1.33–6.58) or a sputum smear positive index case (aOR 3.96, 95% CI 1.20–13.03) were more likely to have TB disease or infection.Conclusions: Prompt TB investigations and early diagnosis can be achieved with a well-organised contact tracing structure. The risk for TB infection or disease was higher among contacts with household exposure, a sputum smear positive index case or born in a TB endemic country. Large-scale investigations among children exposed in congregate settings can result in a very low yield and should be cautiously targeted. What is Known:• Vulnerable young children are a high priority in contact tracing and should be evaluated as soon as possible after TB exposure What is New:• Prompt investigations for paediatric TB contacts and early diagnosis of infected children can be achieved with a well-organised contact tracing structure• Large-scale investigations among children exposed in congregate settings can result in a very low yield and should be cautiously targeted

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Investigation of Four Clusters of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Rwanda, 2020

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18137018 ◽

2021 ◽

Vol 18 (13) ◽

pp. 7018

Author(s):

Olivier Nsekuye ◽

Edson Rwagasore ◽

Marie Aime Muhimpundu ◽

Ziad El-Khatib ◽

Daniel Ntabanganyimana ◽

...

Keyword(s):

High Risk ◽

Severe Acute Respiratory Syndrome ◽

Symptom Onset ◽

Attack Rate ◽

Positive Sample ◽

Contact Tracing ◽

Face To Face ◽

Laboratory Confirmation ◽

Closed Environment ◽

Index Cases

We reported the findings of the first Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) four clusters identified in Rwanda. Case-investigations included contact elicitation, testing, and isolation/quarantine of confirmed cases. Socio-demographic and clinical data on cases and contacts were collected. A confirmed case was a person with laboratory confirmation of SARS-CoV-2 infection (PCR) while a contact was any person who had contact with a SARS-CoV-2 confirmed case within 72 h prior, to 14 days after symptom onset; or 14 days before collection of the laboratory-positive sample for asymptomatic cases. High risk contacts were those who had come into unprotected face-to-face contact or had been in a closed environment with a SARS-CoV-2 case for >15 min. Forty cases were reported from four clusters by 22 April 2020, accounting for 61% of locally transmitted cases within six weeks. Clusters A, B, C and D were associated with two nightclubs, one house party, and different families or households living in the same compound (multi-family dwelling). Thirty-six of the 1035 contacts tested were positive (secondary attack rate: 3.5%). Positivity rates were highest among the high-risk contacts compared to low-risk contacts (10% vs. 2.2%). Index cases in three of the clusters were imported through international travelling. Fifteen of the 40 cases (38%) were asymptomatic while 13/25 (52%) and 8/25 (32%) of symptomatic cases had a cough and fever respectively. Gatherings in closed spaces were the main early drivers of transmission. Systematic case-investigations contact tracing and testing likely contributed to the early containment of SARS-CoV-2 in Rwanda.

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Methicillin-Resistant Staphylococcus aureus Prevalence Among Healthcare Workers in Contact Tracings in a Dutch Hospital

Infection Control and Hospital Epidemiology ◽

10.1017/ice.2020.910 ◽

2020 ◽

Vol 41 (S1) ◽

pp. s316-s317

Author(s):

Veronica Weterings ◽

Heidi Kievits ◽

Miranda van Rijen ◽

Jan Kluytmans

Keyword(s):

Staphylococcus Aureus ◽

The Netherlands ◽

Healthcare Workers ◽

Index Case ◽

Contact Tracing ◽

Secondary Case ◽

National Guidelines ◽

Carriage Rate ◽

Methicillin Resistant ◽

Mlva Type

Background: In The Netherlands, the national guidelines on Methicillin-Resistant Staphylococcus aureus (MRSA) prevention and control advocate screening of healthcare workers (HCWs) after unprotected exposure to MRSA carriers. Although this strategy is largely successful, contact tracing of staff is a time-consuming and costly component. We evaluated our contact tracing policy for HCWs over the years 2010–2018. Methods: A retrospective, observational study was performed in a Dutch teaching hospital. All HCWs who had unprotected contact with an MRSA carrier were included in contact tracing. When there had been a long period of unprotected admission prior to an MRSA finding, or when the index case was an HCW, the entire (nursing) team was tested. All samples of HCWs who were tested for MRSA carriage as part of contact tracing from 2010 until 2018 were included. A pooled nose, throat, and perineum swab was collected using the eSwab medium (Copan) and inoculated on chromID MRSA agar plates (bioMérieux) after enrichment in a broth. Molecular typing was performed using multiple-locus variable number of tandem repeat analysis (MLVA). Results: In total, we included 8,849 samples (range, 677–1,448 samples per year) from 287 contact tracings (range, 26–55 contact tracings per year). Overall, 32 HCWs were colonized with MRSA (0.36%; 95% CI, 0.26%–0.51%). None of them developed a clinical infection. Moreover, 8 HCWs (0.10%; 95% CI, 0.05%–0.19%) were colonized with the same MLVA type as the index case and were detected in 6 of 287 contact tracings (2%). In 4 of 8 of these cases, a positive HCW was the index for undertaking contact tracing. In 3 of 8 cases, it was clear that the HCW who was identified in the contact tracing was the source of the outbreak and was the cause of invasive MRSA infections in patients. Notably, a different MLVA type as the index case was found in 24 HCWs (0.27%; 95% CI, 0.18%–0.40%) of whom 7 of 24 HCWs (29.2%) were intermittent carriers. Conclusions: This study revealed a sustained low MRSA prevalence among samples in contact tracing of HCWs over 9 years. Furthermore, it shows that when MRSA contact tracing is performed according to the national guideline, only 1 of 1,000 samples results in a secondary case. This is similar to the population carriage rate of MRSA in The Netherlands. More frequently, an unrelated strain is found. These findings raise questions regarding the efficacy of the current strategy to perform contact tracing after unprotected exposure.Funding: NoneDisclosures: None

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HTLV-1 infection is associated with a history of active tuberculosis among family members of HTLV-1-infected patients in Peru

Epidemiology and Infection ◽

10.1017/s0950268807009521 ◽

2007 ◽

Vol 136 (8) ◽

pp. 1076-1083 ◽

Cited By ~ 14

Author(s):

K. VERDONCK ◽

E. GONZÁLEZ ◽

W. SCHROOTEN ◽

G. VANHAM ◽

E. GOTUZZO

Keyword(s):

Multivariate Analysis ◽

Index Case ◽

Family Members ◽

Active Tuberculosis ◽

T Lymphotropic Virus ◽

Lifetime History ◽

History Of ◽

Index Cases

SUMMARYThe purpose of this study was to assess the association between human T-lymphotropic virus 1 (HTLV-1) and a lifetime history of active tuberculosis (TB) among relatives of HTLV-1-infected patients. We reviewed clinical charts of all relatives of HTLV-1-infected index cases who attended our institute in Lima from 1990–2004. The data of 1233 relatives was analysed; 394 (32·0%) were HTLV-1 positive. Eighty-one subjects (6·6%) had a history of active TB, including 45/394 (11·4%) HTLV-1-positive and 36/839 (4·3%) HTLV-1-negative relatives (P<0·001). On multivariate analysis, three factors were associated with TB history: HTLV-1 infection (adjusted OR 2·5, 95% CI 1·6–3·9), age (adjusted OR 1·3, 95% CI 1·1–1·5 per 10-year age increase) and relation to the index case (adjusted OR 2·6, 95% CI 1·3–5·1, for siblingsvs. spouses of index cases). In conclusion, HTLV-1 infection may increase the susceptibility to active TB. In populations where both infections are frequent, such an association could affect the dynamics of TB.

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