| 130 | Belgium |
| 109 | Humans |
| 76 | Influenza, Human |
| 67 | Male |
| 66 | Female |
| 48 | Adult |
| 47 | Middle Aged |
| 46 | Aged |
| 35 | Influenza Vaccines |
| 28 | Animals |
| 26 | Disease Outbreaks |
| 25 | Adolescent |
| 24 | Young Adult |
| 23 | Aged, 80 and over |
| 22 | Vaccination |
| 22 | Influenza A virus |
| 21 | Child |
| 20 | Child, Preschool |
| 18 | Influenza A Virus, H1N1 Subtype |
| 16 | Infant |
| 14 | Surveys and Questionnaires |
| 14 | Influenza in Birds |
| 13 | Seasons |
| 13 | Antibodies, Viral |
| 11 | Risk Factors |
| 11 | Retrospective Studies |
| 11 | Netherlands |
| 11 | Cross-Sectional Studies |
| 10 | Population Surveillance |
| 10 | Influenza A Virus, H5N1 Subtype |
| 9 | Sensitivity and Specificity |
| 9 | Prevalence |
| 9 | Infant, Newborn |
| 9 | Incidence |
| 8 | Time Factors |
| 8 | Antiviral Agents |
| 7 | Swine |
| 7 | Sentinel Surveillance |
| 7 | Respiratory Tract Infections |
| 7 | Prospective Studies |
| 7 | Influenza B virus |
| 6 | Seroepidemiologic Studies |
| 6 | Risk Assessment |
| 6 | Pregnancy |
| 6 | Poultry |
| 6 | Patient Acceptance of Health Care |
| 6 | Pandemics |
| 6 | Orthomyxoviridae |
| 6 | Orthomyxoviridae Infections |
| 6 | Logistic Models |
| 6 | Germany |
| 6 | France |
| 6 | Age Factors |
| 5 | Virus Diseases |
| 5 | Swine Diseases |
| 5 | Socioeconomic Factors |
| 5 | Pneumococcal Vaccines |
| 5 | Oseltamivir |
| 5 | Hemagglutination Inhibition Tests |
| 5 | Health Personnel |
| 5 | Health Knowledge, Attitudes, Practice |
| 5 | Family Practice |
| 5 | Europe |
| 5 | Enzyme-Linked Immunosorbent Assay |
| 5 | Cohort Studies |
| 5 | Attitude of Health Personnel |
| 4 | Travel |
| 4 | Regression Analysis |
| 4 | Primary Health Care |
| 4 | Pregnancy Complications, Infectious |
| 4 | Phylogeny |
| 4 | Nursing Homes |
| 4 | Nasopharynx |
| 4 | Multivariate Analysis |
| 4 | Intensive Care Units |
| 4 | Influenza A Virus, H3N2 Subtype |
| 4 | Infection Control |
| 4 | Immunization Programs |
| 4 | Hospitalization |
| 4 | Epidemiological Monitoring |
| 4 | Disaster Planning |
| 4 | Diagnosis, Differential |
| 4 | Denmark |
| 4 | Data Collection |
| 4 | Communicable Disease Control |
| 4 | Birds |
| 4 | Anti-Bacterial Agents |
| 4 | Age Distribution |
| 3 | Vaccines, Inactivated |
| 3 | United Kingdom |
| 3 | Tetanus Toxoid |
| 3 | Switzerland |
| 3 | Statistics, Nonparametric |
| 3 | Smoking |
| 3 | Serotyping |
| 3 | Reverse Transcriptase Polymerase Chain Reaction |
| 3 | Respiratory Tract Diseases |
| 3 | Respiratory Syncytial Viruses |
| 3 | Real-Time Polymerase Chain Reaction |
| 3 | Reagent Kits, Diagnostic |
| 3 | Public Health |
| 3 | Preventive Health Services |
| 3 | Practice Patterns, Physicians' |
| 3 | Portugal |
| 3 | Polymerase Chain Reaction |
| 3 | Pneumonia, Viral |
| 3 | Odds Ratio |
| 3 | Models, Theoretical |
| 3 | Models, Statistical |
| 3 | Internet |
| 3 | Immunization |
| 3 | Immunization Schedule |
| 3 | Hospitals |
| 3 | Health Surveys |
| 3 | Guideline Adherence |
| 3 | Genetic Variation |
| 3 | General Practitioners |
| 3 | Epidemics |
| 3 | England |
| 3 | Educational Status |
| 3 | Drug-Related Side Effects and Adverse Reactions |
| 3 | Croatia |
| 3 | Common Cold |
| 3 | Chi-Square Distribution |
| 3 | Canada |
| 3 | Austria |
| 3 | Antibodies, Bacterial |
| 3 | Animal Husbandry |
| 2 | alpha-Tocopherol |
| 2 | Zoonoses |
| 2 | Whooping Cough |
| 2 | Virulence |
| 2 | Virology |
| 2 | Vaccines, Conjugate |
| 2 | Vaccines, Attenuated |
| 2 | Vaccination Coverage |
| 2 | Treatment Outcome |
| 2 | Survival Analysis |
| 2 | Students, Medical |
| 2 | Streptococcus pneumoniae |
| 2 | Squalene |
| 2 | Spain |
| 2 | Social Behavior |
| 2 | Smoking Prevention |
| 2 | Risk |
| 2 | Renal Dialysis |
| 2 | Registries |
| 2 | Random Allocation |
| 2 | RNA, Viral |
| 2 | Quality of Health Care |
| 2 | Pseudorabies |
| 2 | Probability |
| 2 | Pregnant Women |
| 2 | Predictive Value of Tests |
| 2 | Practice Guidelines as Topic |
| 2 | Poultry Diseases |
| 2 | Population Control |
| 2 | Polysorbates |
| 2 | Pneumonia, Pneumococcal |
| 2 | Pilot Projects |
| 2 | Physicians, Family |
| 2 | Pharmacies |
| 2 | Pertussis Vaccine |
| 2 | Patient Admission |
| 2 | Neuraminidase |
| 2 | National Health Programs |
| 2 | Nasal Mucosa |
| 2 | Myocardial Infarction |
| 2 | Mortality |
| 2 | Molecular Sequence Data |
| 2 | Molecular Epidemiology |
| 2 | Molecular Diagnostic Techniques |
| 2 | Models, Economic |
| 2 | Military Personnel |
| 2 | Military Medicine |
| 2 | Livestock |
| 2 | Laboratories |
| 2 | Japan |
| 2 | Italy |
| 2 | Invasive Pulmonary Aspergillosis |
| 2 | Interviews as Topic |
| 2 | Injections, Intradermal |
| 2 | Influenza A Virus, H7N7 Subtype |
| 2 | Hospitals, University |
| 2 | Hospital Mortality |
| 2 | Hemagglutination Tests |
| 2 | Health Services Needs and Demand |
| 2 | Health Education |
| 2 | Haemophilus Vaccines |
| 2 | Genome, Viral |
| 2 | Gastrointestinal Diseases |
| 2 | Follow-Up Studies |
| 2 | Extracorporeal Membrane Oxygenation |
| 2 | Evaluation Studies as Topic |
| 2 | Environmental Monitoring |
| 2 | Emergency Service, Hospital |
| 2 | Ducks |
| 2 | Drug Combinations |
| 2 | Disease Notification |
| 2 | Diphtheria-Tetanus-Pertussis Vaccine |
| 2 | Diabetes Mellitus |
| 2 | Decision Making |
| 2 | Czech Republic |
| 2 | Cross Infection |
| 2 | Critical Care |
| 2 | Cost-Benefit Analysis |
| 2 | Community-Acquired Infections |
| 2 | Communicable Diseases |
| 2 | Clinical Competence |
| 2 | Case-Control Studies |
| 2 | Bird Diseases |
| 2 | Biomarkers |
| 2 | Antigens, Viral |
| 2 | Antibodies, Neutralizing |
| 2 | Anseriformes |
| 2 | Animals, Wild |
| 1 | Zanamivir |
| 1 | Yersinia enterocolitica |
| 1 | World War I |
| 1 | World Health Organization |
| 1 | Workplace |
| 1 | Wales |
| 1 | Viruses |
| 1 | Viral Vaccines |
| 1 | Viral Load |
| 1 | Ventricular Dysfunction, Right |
| 1 | Ventricular Dysfunction, Left |
| 1 | Vaginal Smears |
| 1 | Vaccines, Combined |
| 1 | Uterine Cervical Neoplasms |
| 1 | Uncertainty |
| 1 | Turkeys |
| 1 | Turkey |
| 1 | Transmissible gastroenteritis virus |
| 1 | Touch |
| 1 | Tobacco Smoke Pollution |
| 1 | Thailand |
| 1 | Text Messaging |
| 1 | Tertiary Care Centers |
| 1 | Temperature |
| 1 | Syringes |
| 1 | Sweden |
| 1 | Survival Rate |
| 1 | Superinfection |
| 1 | Statistics as Topic |
| 1 | Staphylococcus aureus |
| 1 | Specimen Handling |
| 1 | Space-Time Clustering |
| 1 | Social Networking |
| 1 | Smoking Cessation |
| 1 | Smoke-Free Policy |
| 1 | Slovenia |
| 1 | Slovakia |
| 1 | Single-Blind Method |
| 1 | Sex Factors |
| 1 | Severe Acute Respiratory Syndrome |
| 1 | Serologic Tests |
| 1 | Sequence Analysis |
| 1 | Sequence Analysis, RNA |
| 1 | Sequence Analysis, DNA |
| 1 | Self Report |
| 1 | Scotland |
| 1 | Schools |
| 1 | Safety |
| 1 | Safety Management |
| 1 | SARS Virus |
| 1 | Rural Population |
| 1 | Rotavirus |
| 1 | Romania |
| 1 | Risk Management |
| 1 | Restaurants |
| 1 | Respirovirus |
| 1 | Respirovirus Infections |
| 1 | Respiratory Syncytial Virus, Human |
| 1 | Respiratory Syncytial Virus Infections |
| 1 | Respiratory Distress Syndrome, Adult |
| 1 | Reproducibility of Results |
| 1 | Reminder Systems |
| 1 | Raptors |
| 1 | ROC Curve |
| 1 | RNA, Ribosomal, 16S |
| 1 | Quality-Adjusted Life Years |
| 1 | Quality of Life |
| 1 | Qualitative Research |
| 1 | Pulmonary Disease, Chronic Obstructive |
| 1 | Public Health Surveillance |
| 1 | Public Health Practice |
| 1 | Public Health Informatics |
| 1 | Protein Conformation |
| 1 | Program Evaluation |
| 1 | Prognosis |
| 1 | Product Surveillance, Postmarketing |
| 1 | Probiotics |
| 1 | Premature Birth |
| 1 | Pregnancy Trimesters |
| 1 | Pregnancy Trimester, Third |
| 1 | Pre-Exposure Prophylaxis |
| 1 | Postpartum Period |
| 1 | Poland |
| 1 | Poisson Distribution |
| 1 | Point-of-Care Systems |
| 1 | Pneumonia |
| 1 | Pneumonia, Bacterial |
| 1 | Pneumonia of Swine, Mycoplasmal |
| 1 | Placebos |
| 1 | Phylogeography |
| 1 | Photography |
| 1 | Pharynx |
| 1 | Pharmaceutical Preparations |
| 1 | Pets |
| 1 | Personnel, Hospital |
| 1 | Percutaneous Coronary Intervention |
| 1 | Perception |
| 1 | Patient-Centered Care |
| 1 | Patient Satisfaction |
| 1 | Patient Safety |
| 1 | Patient Preference |
| 1 | Parvoviridae Infections |
| 1 | Paris |
| 1 | Papanicolaou Test |
| 1 | Ownership |
| 1 | Opportunistic Infections |
| 1 | Online Systems |
| 1 | Nucleic Acid Amplification Techniques |
| 1 | Norway |
| 1 | Northern Ireland |
| 1 | Nonlinear Dynamics |
| 1 | Nocardia |
| 1 | Nocardia Infections |
| 1 | Newspapers as Topic |
| 1 | Neutralization Tests |
| 1 | Nervous System Diseases |
| 1 | Mycoplasma |
| 1 | Mycoplasma Infections |
| 1 | Morbidity |
| 1 | Moraxella catarrhalis |
| 1 | Mongolia |
| 1 | Models, Molecular |
| 1 | Models, Genetic |
| 1 | Models, Econometric |
| 1 | Models, Biological |
| 1 | Milk |
| 1 | Military Nursing |
| 1 | Microbial Sensitivity Tests |
| 1 | Mice |
| 1 | Mice, Inbred BALB C |
| 1 | Metered Dose Inhalers |
| 1 | Metapneumovirus |
| 1 | Memory |
| 1 | Medication Errors |
| 1 | Medication Adherence |
| 1 | Mass Vaccination |
| 1 | Mass Screening |
| 1 | Mass Media |
| 1 | Mammography |
| 1 | Malaria |
| 1 | Malaria, Falciparum |
| 1 | Lung |
| 1 | Lung Transplantation |
| 1 | London |
| 1 | Linear Models |
| 1 | Lactobacillus casei |
| 1 | Kidney Transplantation |
| 1 | Kidney Failure, Chronic |
| 1 | Ireland |
| 1 | Interpersonal Relations |
| 1 | Internationality |
| 1 | International Cooperation |
| 1 | International Agencies |
| 1 | Interinstitutional Relations |
| 1 | Interdisciplinary Communication |
| 1 | Intention |
| 1 | Insurance Claim Review |
| 1 | Influenza A Virus, H5N2 Subtype |
| 1 | Influenza A Virus, H3N8 Subtype |
| 1 | Infectious Disease Transmission, Professional-to-Patient |
| 1 | Infant, Premature |
| 1 | Indonesia |
| 1 | Inappropriate Prescribing |
| 1 | Immunosuppressive Agents |
| 1 | Immunoassay |
| 1 | Immunization, Secondary |
| 1 | Immunity, Humoral |
| 1 | Immunity, Cellular |
| 1 | Hypercholesterolemia |
| 1 | Hungary |
| 1 | Human bocavirus |
| 1 | Hospitals, Military |
| 1 | Hospitals, Convalescent |
| 1 | Hospital Costs |
| 1 | Horses |
| 1 | Horse Diseases |
| 1 | Holidays |
| 1 | History, 21st Century |
| 1 | History, 20th Century |
| 1 | History of Medicine |
| 1 | Histocompatibility Antigens Class II |
| 1 | Histocompatibility Antigens Class I |
| 1 | High-Throughput Nucleotide Sequencing |
| 1 | Herpesvirus 1, Suid |
| 1 | Hemodynamics |
| 1 | Hemagglutinins |
| 1 | Healthy Volunteers |
| 1 | Health Services for the Aged |
| 1 | Health Services Research |
| 1 | Health Services Accessibility |
| 1 | Health Priorities |
| 1 | Health Policy |
| 1 | Hand Hygiene |
| 1 | Haemophilus influenzae |
| 1 | Guidelines as Topic |
| 1 | Glucocorticoids |
| 1 | Global Health |
| 1 | Geriatric Assessment |
| 1 | Genotype |
| 1 | Forecasting |
| 1 | Fever |
| 1 | Fermentation |
| 1 | Feasibility Studies |
| 1 | Family Characteristics |
| 1 | Epitopes |
| 1 | Environmental Exposure |
| 1 | Electronic Mail |
| 1 | Electronic Health Records |
| 1 | Electrocardiography |
| 1 | Educational Measurement |
| 1 | Education, Medical, Undergraduate |
| 1 | Ecosystem |
| 1 | Economics |
| 1 | Echocardiography |
| 1 | Early Detection of Cancer |
| 1 | Drug Resistance, Bacterial |
| 1 | Double-Blind Method |
| 1 | Disease Susceptibility |
| 1 | Disaster Medicine |
| 1 | Diagnostic Tests, Routine |
| 1 | Diabetes Complications |
| 1 | Decision Support Techniques |
| 1 | Databases, Factual |
| 1 | DNA, Viral |
| 1 | Curriculum |
| 1 | Cross-Cultural Comparison |
| 1 | Cross Reactions |
| 1 | Critical Illness |
| 1 | Crime |
| 1 | Cost of Illness |
| 1 | Correspondence as Topic |
| 1 | Cooperative Behavior |
| 1 | Contact Tracing |
| 1 | Computer Communication Networks |
| 1 | Computational Biology |
| 1 | Comorbidity |
| 1 | Community Pharmacy Services |
| 1 | Cognition |
| 1 | Cluster Analysis |
| 1 | Cloning, Molecular |
| 1 | Clinical Laboratory Techniques |
| 1 | Climate |
| 1 | Classical Swine Fever |
| 1 | Chronic Disease |
| 1 | Chromatography, Affinity |
| 1 | China |
| 1 | Chile |
| 1 | Child, Hospitalized |
| 1 | Chikungunya virus |
| 1 | Chemoprevention |
| 1 | Charadriiformes |
| 1 | Carrier State |
| 1 | Cardiac Output |
| 1 | Campylobacter |
| 1 | CD4-Positive T-Lymphocytes |
| 1 | Bronchoalveolar Lavage Fluid |
| 1 | Breast Neoplasms |
| 1 | Blood Chemical Analysis |
| 1 | Berlin |
| 1 | Bayes Theorem |
| 1 | Base Sequence |
| 1 | Bacterial Vaccines |
| 1 | Bacterial Typing Techniques |
| 1 | Bacterial Infections |
| 1 | Avulavirus |
| 1 | Avulavirus Infections |
| 1 | Aviation |
| 1 | Audiovisual Aids |
| 1 | Attitude to Health |
| 1 | Aspergillus |
| 1 | Area Under Curve |
| 1 | Antimalarials |
| 1 | Antibodies |
| 1 | Antibiotic Prophylaxis |
| 1 | Anniversaries and Special Events |
| 1 | Animals, Domestic |
| 1 | Animal Migration |
| 1 | Analysis of Variance |
| 1 | Ambulatory Care |
| 1 | Ambulances |
| 1 | Alphavirus Infections |
| 1 | Aleutian Mink Disease Virus |
| 1 | Air Pollution |
| 1 | Agriculture |
