Importance of cough and M. tuberculosis strain type as risks for increased transmission within households.

RATIONALE: The degree to which tuberculosis (TB) is transmitted between persons is variable. Identifying the factors that contribute to transmission could provide new opportunities for TB control. Transmission is influenced by host, bacterial and environmental factors. However, distinguishing their individual effects is problematic because measures of disease severity are tightly correlated, and assessing the virulence of Mycobacterium tuberculosis isolates is complicated by epidemiological and clinical confounders. OBJECTIVES: To overcome these problems, we investigated factors potentially associated with TB transmission within households. METHODS: We evaluated patients with smear-positive (≥2+), pulmonary TB and classified M. tuberculosis strains into single nucleotide polymorphism genetic cluster groups (SCG). We recorded index case, household contact, and environmental characteristics and tested contacts with tuberculin skin test (TST) and interferon-gamma release assay. Households were classified as high (≥70% of contacts with TST≥10 mm) and low (≤40%) transmission. We used logistic regression to determine independent predictors. RESULT: From March 2008 to June 2012, we screened 293 TB patients to enroll 124 index cases and their 731 contacts. There were 23 low and 73 high transmission households. Index case factors associated with high transmission were severity of cough as measured by a visual analog cough scale (VACS) and the Leicester Cough Questionnaire (LCQ), and cavitation on chest radiograph. SCG 3b strains tended to be more prevalent in low (27.3%) than in high (12.5%) transmission households (p = 0.11). In adjusted models, only VACS (p<0.001) remained significant. SCG was associated with bilateral disease on chest radiograph (p = 0.002) and marginally associated with LCQ sores (p = 0.058), with group 3b patients having weaker cough. CONCLUSIONS: We found differential transmission among otherwise clinically similar patients with advanced TB disease. We propose that distinct strains may cause differing patterns of cough strength and cavitation in the host leading to diverging infectiousness. Larger studies are needed to verify this hypothesis.

Juvenile household contacts aged 15 or younger of patients with pulmonary TB in the greater metropolitan area of Vitória, Brazil: a cohort study.

OBJECTIVE: To compare clinical, radiological and laboratory aspects of household contacts, aged 15 or younger, of patients presenting a positive culture for Mycobacterium tuberculosis. METHODS: This was a cohort study comparing children and adolescents (< or = 15 years of age) who were household contacts of TB cases presenting positive sputum smear and positive culture results (exposed group, n = 100) or negative sputum smear and positive culture results (unexposed group, n = 55). All of the contacts were evaluated via the TB control program of a university hospital in the city of Vitória, Brazil, between July of 2003 and December of 2006. RESULTS: Of the 155 minors evaluated, 87 (56.1%) were female and 68 (43.9%) were male. Of those 155, 28 (18%) were aged 5 or younger, 62 (40%) were aged 5-9, and 65 (42%) were aged 10-15. Symptoms of the disease were found in 17 (17%) of the 100 contacts in the exposed group and in 9 (16%) of the 55 in the unexposed group (p = 0.86). Chest X-rays showed alterations in 20 (21%) and 2 (4%) of the contacts in the exposed and unexposed groups, respectively (RR = 6.9; p = 0.004). In the exposed and unexposed groups, respectively, 35 (38%) and 10 (18%) of the contacts presented positive results in the tuberculin skin test (RR = 2.8; p = 0.01). Of the 100 contacts in the exposed group, 5 (5%) were diagnosed with TB, which was not diagnosed in any of those in the unexposed group (p = 0.08). CONCLUSIONS: Although no significant difference was found between the two groups regarding the incidence of TB, it is of note that there is a greater risk of becoming infected with M. tuberculosis if the bacterial load of the index case is high.

Comunicantes domiciliares jovens de pacientes com TB pulmonar na região da grande Vitória (ES): um estudo de coorte / Juvenile household contacts aged 15 or younger of patients with pulmonary TB in the greater metropolitan area of Vitória, Brazil: a cohort study

OBJETIVO: Comparar aspectos clínicos, radiológicos e laboratoriais de contatos domiciliares, menores de 15 anos, de pacientes com cultura positiva para Mycobacterium tuberculosis. MÉTODOS: Realizou-se um estudo de coorte comparando crianças e adolescentes (< 15 anos) que eram contatos domiciliares de casos de TB com baciloscopia e cultura positiva (grupo exposto, n = 100) ou com baciloscopia negativa e cultura positiva (grupo não-exposto, n = 55). Todos os contatos foram avaliados no período de julho de 2003 a dezembro de 2006, no programa de controle da TB de um hospital universitário na cidade de Vitória (ES). RESULTADOS: Das 155 contatos avaliados, 87 (56,1 por cento) eram do sexo feminino e 68 (43,9 por cento) do masculino. Do total, 28 (18 por cento) eram menores de 5 anos; 62 (40 por cento), entre 5-9 anos; e 65 (42 por cento), entre 10-15 anos. Foi detectada a presença de sintomas de TB em 17 (17 por cento) dos 100 contatos no grupo exposto e em 9 (16 por cento) dos 55 no grupo não-exposto (p = 0,86). A radiografia de tórax apresentou alterações em 20 (21 por cento) e 2 (4 por cento) dos contatos nos grupos exposto e não-exposto, respectivamente (RR = 6,9; p = 0,004). Nos grupos exposto e não-exposto, respectivamente, 35 (38 por cento) e 10 (18 por cento) dos contatos apresentaram prova tuberculínica positiva (RR = 2,8; p = 0,01). No total, 5 contatos (5 por cento) do grupo exposto foram diagnosticados com TB, ao passo que não houve diagnóstico de TB no grupo não-exposto (p = 0,08). CONCLUSÕES: Apesar desta pesquisa não ter encontrado diferença significativa no surgimento de casos de TB entre os comunicantes dos grupos estudados, deve-se ressaltar que quanto maior a carga bacilar do caso índice, maior é a chance dos seus contatos virem a se infectar por M. tuberculosis.

OBJECTIVE: To compare clinical, radiological and laboratory aspects of household contacts, aged 15 or younger, of patients presenting a positive culture for Mycobacterium tuberculosis. METHODS: This was a cohort study comparing children and adolescents (< 15 years of age) who were household contacts of TB cases presenting positive sputum smear and positive culture results (exposed group, n = 100) or negative sputum smear and positive culture results (unexposed group, n = 55). All of the contacts were evaluated via the TB control program of a university hospital in the city of Vitória, Brazil, between July of 2003 and December of 2006. RESULTS: Of the 155 minors evaluated, 87 (56.1 percent) were female and 68 (43.9 percent) were male. Of those 155, 28 (18 percent) were aged 5 or younger, 62 (40 percent) were aged 5-9, and 65 (42 percent) were aged 10-15. Symptoms of the disease were found in 17 (17 percent) of the 100 contacts in the exposed group and in 9 (16 percent) of the 55 in the unexposed group (p = 0.86). Chest X-rays showed alterations in 20 (21 percent) and 2 (4 percent) of the contacts in the exposed and unexposed groups, respectively (RR = 6.9; p = 0.004). In the exposed and unexposed groups, respectively, 35 (38 percent) and 10 (18 percent) of the contacts presented positive results in the tuberculin skin test (RR = 2.8; p = 0.01). Of the 100 contacts in the exposed group, 5 (5 percent) were diagnosed with TB, which was not diagnosed in any of those in the unexposed group (p = 0.08). CONCLUSIONS: Although no significant difference was found between the two groups regarding the incidence of TB, it is of note that there is a greater risk of becoming infected with M. tuberculosis if the bacterial load of the index case is high.