title: Common infectious agents and monoclonal B-cell lymphocytosis: a cross-sectional epidemiological study among healthy adults.
abstract: BACKGROUND
  Risk factors associated with monoclonal B-cell lymphocytosis (MBL), a potential precursor of chronic lymphocytic leukaemia (CLL), remain unknown.
  
  
  METHODS
  Using a cross-sectional study design, we investigated demographic, medical and behavioural risk factors associated with MBL. "Low-count" MBL (cases) were defined as individuals with very low median absolute count of clonal B-cells, identified from screening of healthy individuals and the remainder classified as controls. 452 individuals completed a questionnaire with their general practitioner, both blind to the MBL status of the subject. Odds ratios (OR) and 95% confidence interval (CI) for MBL were estimated by means of unconditional logistic regression adjusted for confounding factors.
  
  
  RESULTS
  MBL were detected in 72/452 subjects (16%). Increasing age was strongly associated with MBL (P-trend<0.001). MBL was significantly less common among individuals vaccinated against pneumococcal or influenza (OR 0.49, 95% confidence interval (CI): 0.25 to 0.95; P-value=0.03 and OR: 0.52, 95% CI: 0.29 to 0.93, P-value=0.03, respectively). Albeit based on small numbers, cases were more likely to report infectious diseases among their children, respiratory disease among their siblings and personal history of pneumonia and meningitis. No other distinguishing epidemiological features were identified except for family history of cancer and an inverse relationship with diabetes treatment. All associations described above were retained after restricting the analysis to CLL-like MBL.
  
  
  CONCLUSIONS
  Overall, these findings suggest that exposure to infectious agents leading to serious clinical manifestations in the patient or its surroundings may trigger immune events leading to MBL. This exploratory study provides initial insights and directions for future research related to MBL, a potential precursor of chronic lymphocytic leukaemia. Further work is warranted to confirm these findings.
authors.affiliation: Unit of Infections and Cancer, IDIBELL, Institut Català d' Oncologia, L' Hospitalet de Llobregat, Barcelona, Spain. dcasabonne@iconcologia.net
authors.forename: Delphine
authors.initials: D
authors.lastname: Casabonne
authors.forename: Julia
authors.initials: J
authors.lastname: Almeida
authors.forename: Wendy G
authors.initials: WG
authors.lastname: Nieto
authors.forename: Alfonso
authors.initials: A
authors.lastname: Romero
authors.forename: Paulino
authors.initials: P
authors.lastname: Fernández-Navarro
authors.forename: Arancha
authors.initials: A
authors.lastname: Rodriguez-Caballero
authors.forename: Santiago
authors.initials: S
authors.lastname: Muñoz-Criado
authors.forename: Marcos González
authors.initials: MG
authors.lastname: Díaz
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Benavente
authors.forename: Silvia
authors.initials: S
authors.lastname: de Sanjosé
authors.forename: Alberto
authors.initials: A
authors.lastname: Orfao
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001402:B-Lymphocytes / Q000378:metabolism; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000453:epidemiology / Q000209:etiology; D018655:Lymphocyte Count; D008218:Lymphocytosis / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015995:Prevalence; D012307:Risk Factors