| 378 | Brazil |
| 336 | Humans |
| 230 | Influenza, Human |
| 218 | Female |
| 197 | Male |
| 143 | Middle Aged |
| 140 | Adult |
| 113 | Child, Preschool |
| 112 | Influenza A Virus, H1N1 Subtype |
| 108 | Adolescent |
| 104 | Aged |
| 100 | Infant |
| 97 | Child |
| 95 | Influenza Vaccines |
| 76 | Young Adult |
| 60 | Seasons |
| 58 | Pandemics |
| 57 | Vaccination |
| 53 | Respiratory Tract Infections |
| 53 | Animals |
| 53 | Aged, 80 and over |
| 48 | Infant, Newborn |
| 46 | Cross-Sectional Studies |
| 42 | Influenza A virus |
| 39 | Disease Outbreaks |
| 37 | Hospitalization |
| 34 | Risk Factors |
| 33 | Prospective Studies |
| 29 | Orthomyxoviridae Infections |
| 29 | Incidence |
| 28 | Socioeconomic Factors |
| 28 | Prevalence |
| 28 | Pregnancy |
| 28 | Antibodies, Viral |
| 25 | Time Factors |
| 24 | Age Distribution |
| 23 | Reverse Transcriptase Polymerase Chain Reaction |
| 23 | RNA, Viral |
| 22 | Phylogeny |
| 21 | Retrospective Studies |
| 21 | Acute Disease |
| 20 | Population Surveillance |
| 20 | Orthomyxoviridae |
| 20 | Influenza B virus |
| 19 | Hemagglutination Inhibition Tests |
| 19 | Antiviral Agents |
| 18 | Respiratory Syncytial Virus Infections |
| 17 | Virus Diseases |
| 16 | Swine |
| 16 | Swine Diseases |
| 16 | Severity of Illness Index |
| 15 | Influenza A Virus, H3N2 Subtype |
| 15 | Age Factors |
| 14 | Urban Population |
| 14 | Pregnancy Complications, Infectious |
| 14 | Oseltamivir |
| 13 | Immunization Programs |
| 13 | History, 20th Century |
| 13 | Cohort Studies |
| 12 | Rhinovirus |
| 12 | Epidemiological Monitoring |
| 12 | Coinfection |
| 11 | Sequence Analysis, DNA |
| 11 | Respiratory Syncytial Viruses |
| 11 | Health Personnel |
| 10 | Nasopharynx |
| 10 | Molecular Sequence Data |
| 10 | Mass Vaccination |
| 10 | Community-Acquired Infections |
| 9 | Treatment Outcome |
| 9 | Sex Distribution |
| 9 | Respiratory Tract Diseases |
| 9 | Respiratory Syncytial Virus, Human |
| 9 | Public Health |
| 9 | Paramyxoviridae Infections |
| 9 | Neuraminidase |
| 9 | Hemagglutinin Glycoproteins, Influenza Virus |
| 9 | Fluorescent Antibody Technique, Indirect |
| 9 | Comorbidity |
| 8 | Viruses |
| 8 | Seroepidemiologic Studies |
| 8 | Pneumonia |
| 8 | Hospitals, University |
| 8 | Cross Infection |
| 8 | Antigens, Viral |
| 7 | Tropical Climate |
| 7 | Tetanus Toxoid |
| 7 | Surveys and Questionnaires |
| 7 | Sentinel Surveillance |
| 7 | Real-Time Polymerase Chain Reaction |
| 7 | Polymerase Chain Reaction |
| 7 | Pneumonia, Viral |
| 7 | Picornaviridae Infections |
| 7 | Mutation |
| 7 | Models, Biological |
| 7 | Logistic Models |
| 7 | Influenza in Birds |
| 7 | Health Status |
| 7 | Health Knowledge, Attitudes, Practice |
| 7 | Haemophilus Vaccines |
| 7 | HIV Infections |
| 7 | Genetic Variation |
| 7 | Epidemics |
| 7 | Chronic Disease |
| 7 | Adenoviridae |
| 6 | Viral Load |
| 6 | Travel |
| 6 | Statistics, Nonparametric |
| 6 | Sex Factors |
| 6 | Risk Assessment |
| 6 | Pneumococcal Vaccines |
| 6 | Multivariate Analysis |
| 6 | Mice |
| 6 | Lung |
| 6 | Horses |
| 6 | Horse Diseases |
| 6 | Health Surveys |
| 6 | Health Services for the Aged |
| 6 | Health Promotion |
| 6 | Genome, Viral |
| 6 | Drug Resistance, Viral |
| 6 | Case-Control Studies |
| 6 | Birds |
| 6 | Argentina |
| 6 | Adenovirus Infections, Human |
| 5 | United States |
| 5 | Serologic Tests |
| 5 | Respirovirus |
| 5 | Regression Analysis |
| 5 | Patient Compliance |
| 5 | Nasal Lavage Fluid |
| 5 | Metapneumovirus |
| 5 | Influenza A Virus, H3N8 Subtype |
| 5 | Influenza A Virus, H1N2 Subtype |
| 5 | Immunosuppressive Agents |
| 5 | Immunization Schedule |
| 5 | Genotype |
| 5 | Fever |
| 5 | Disease Notification |
| 5 | Cost-Benefit Analysis |
| 5 | Coronavirus Infections |
| 5 | Chi-Square Distribution |
| 5 | Cause of Death |
| 5 | Bird Diseases |
| 5 | Antibodies, Bacterial |
| 5 | Animal Migration |
| 4 | Zika Virus |
| 4 | Zika Virus Infection |
| 4 | Viral Proteins |
| 4 | Vaccines, Conjugate |
| 4 | Vaccines, Combined |
| 4 | Vaccination Coverage |
| 4 | Students, Medical |
| 4 | Spatio-Temporal Analysis |
| 4 | Sensitivity and Specificity |
| 4 | Risk |
| 4 | Pregnancy Outcome |
| 4 | Pneumonia, Bacterial |
| 4 | Patient Acceptance of Health Care |
| 4 | Morbidity |
| 4 | Molecular Epidemiology |
| 4 | Intensive Care Units |
| 4 | Indians, South American |
| 4 | Hospitals, Teaching |
| 4 | Hospital Mortality |
| 4 | Hemagglutination Tests |
| 4 | Health Policy |
| 4 | Haemophilus influenzae |
| 4 | Guideline Adherence |
| 4 | Gestational Age |
| 4 | Epidemiologic Methods |
| 4 | Dengue |
| 4 | Death Certificates |
| 4 | Databases, Factual |
| 4 | Cough |
| 4 | Chile |
| 4 | Biomarkers |
| 4 | Animals, Wild |
| 4 | Adenoviridae Infections |
| 3 | Vaccines |
| 3 | Treatment Refusal |
| 3 | Tertiary Care Centers |
| 3 | Sus scrofa |
| 3 | South Africa |
| 3 | Ships |
| 3 | Severe Acute Respiratory Syndrome |
| 3 | Self Report |
| 3 | Respiratory Distress Syndrome, Adult |
| 3 | Public Health Surveillance |
| 3 | Program Evaluation |
| 3 | Prognosis |
| 3 | Poisson Distribution |
| 3 | Pneumonia, Pneumococcal |
| 3 | Parainfluenza Virus 3, Human |
| 3 | Oropharynx |
| 3 | Occupational Diseases |
| 3 | Mortality |
| 3 | Models, Statistical |
| 3 | Microscopy, Electron |
| 3 | Maternal Mortality |
| 3 | Lupus Erythematosus, Systemic |
| 3 | Longitudinal Studies |
| 3 | Kidney Transplantation |
| 3 | Intensive Care Units, Pediatric |
| 3 | Infection Control |
| 3 | Immunocompromised Host |
| 3 | Hospitals |
| 3 | Hemagglutinins |
| 3 | Haemophilus influenzae type b |
| 3 | Haemophilus Infections |
| 3 | Follow-Up Studies |
| 3 | Fatal Outcome |
| 3 | Enzyme-Linked Immunosorbent Assay |
| 3 | Educational Status |
| 3 | Dogs |
| 3 | Disease Transmission, Infectious |
| 3 | Diphtheria-Tetanus-Pertussis Vaccine |
| 3 | Data Collection |
| 3 | Cluster Analysis |
| 3 | Chick Embryo |
| 3 | CD4 Lymphocyte Count |
| 3 | Bronchoalveolar Lavage Fluid |
| 3 | Betacoronavirus |
| 3 | Bacterial Infections |
| 3 | Australia |
| 3 | Attitude to Health |
| 3 | Attitude of Health Personnel |
| 3 | Asthma |
| 3 | Antibodies |
| 3 | Animal Husbandry |
| 3 | Amino Acid Substitution |
| 3 | Ambulatory Care |
| 3 | Adverse Drug Reaction Reporting Systems |
| 3 | Adenoviruses, Human |
| 3 | Absenteeism |
| 2 | Workplace |
| 2 | Weight Loss |
| 2 | Virus Cultivation |
| 2 | Virulence Factors |
| 2 | Vaccines, Inactivated |
| 2 | United Kingdom |
| 2 | USSR |
| 2 | Travel Medicine |
| 2 | Toxoplasmosis |
| 2 | Temperature |
| 2 | Streptococcus pneumoniae |
| 2 | Staphylococcus aureus |
| 2 | Spain |
| 2 | Serotyping |
| 2 | Sequence Deletion |
| 2 | Sequence Analysis |
| 2 | Sanitation |
| 2 | Rural Population |
| 2 | Respiratory System |
| 2 | Respiratory Sounds |
| 2 | Respiration, Artificial |
| 2 | Respiration Disorders |
| 2 | Reproducibility of Results |
| 2 | Referral and Consultation |
| 2 | Receptors, CCR5 |
| 2 | Rain |
| 2 | Quality-Adjusted Life Years |
| 2 | Propolis |
| 2 | Prenatal Care |
| 2 | Premature Birth |
| 2 | Pregnant Women |
| 2 | Polymorphism, Single Nucleotide |
| 2 | Polymorphism, Genetic |
| 2 | Politics |
| 2 | Pneumococcal Infections |
| 2 | Plant Extracts |
| 2 | Physicians |
| 2 | Phylogeography |
| 2 | Parainfluenza Virus 2, Human |
| 2 | Outpatients |
| 2 | Outcome Assessment, Health Care |
| 2 | Odds Ratio |
| 2 | Nose |
| 2 | New Zealand |
| 2 | Neoplasms |
| 2 | Myocardial Ischemia |
| 2 | Mycoplasma hyopneumoniae |
| 2 | Multiplex Polymerase Chain Reaction |
| 2 | Military Personnel |
| 2 | Microcephaly |
| 2 | Methods |
| 2 | Meteorological Concepts |
| 2 | Meningitis, Haemophilus |
| 2 | Medication Adherence |
| 2 | Mass Screening |
| 2 | Lung Diseases |
| 2 | Life Style |
| 2 | Leukocytes, Mononuclear |
| 2 | Length of Stay |
| 2 | Internet |
| 2 | Internationality |
| 2 | Information Dissemination |
| 2 | Influenzavirus B |
| 2 | Influenzavirus A |
| 2 | Influenza A Virus, H7N7 Subtype |
| 2 | Infectious Disease Transmission, Professional-to-Patient |
| 2 | Infectious Disease Transmission, Patient-to-Professional |
| 2 | Infections |
| 2 | Immunoglobulin G |
| 2 | Immunization |
| 2 | Hepatitis B |
| 2 | Hepatitis B Vaccines |
| 2 | Hemorrhagic Fever, Ebola |
| 2 | Hemagglutinins, Viral |
| 2 | Health Status Indicators |
| 2 | Health Education |
| 2 | Health Behavior |
| 2 | Global Health |
| 2 | Geriatric Assessment |
| 2 | Geography |
| 2 | Geography, Medical |
| 2 | Genetic Predisposition to Disease |
| 2 | Genes, Viral |
| 2 | Gene Frequency |
| 2 | France |
| 2 | Fourier Analysis |
| 2 | Fluorescent Antibody Technique |
| 2 | Feces |
| 2 | Farms |
| 2 | Ethnic Groups |
| 2 | Epitopes |
| 2 | Emergency Service, Hospital |
| 2 | Electronic Health Records |
| 2 | Double-Blind Method |
| 2 | Dose-Response Relationship, Immunologic |
| 2 | Disease Susceptibility |
| 2 | Disease Progression |
| 2 | Diphtheria-Tetanus-acellular Pertussis Vaccines |
| 2 | Diabetes Complications |
| 2 | Developing Countries |
| 2 | Decision Support Techniques |
| 2 | DNA, Viral |
| 2 | Coronavirus |
| 2 | Complement Fixation Tests |
| 2 | Communicable Diseases |
| 2 | Communicable Disease Control |
| 2 | Colombia |
| 2 | Climate |
| 2 | Chromatography, High Pressure Liquid |
| 2 | China |
| 2 | Charadriiformes |
| 2 | Cerebrovascular Disorders |
| 2 | Cerebrospinal Fluid |
| 2 | Cell Line |
| 2 | Cell Culture Techniques |
| 2 | Carrier State |
| 2 | C-Reactive Protein |
| 2 | Bronchiolitis |
| 2 | Breast Feeding |
| 2 | Base Sequence |
| 2 | Bacterial Vaccines |
| 2 | BCG Vaccine |
| 2 | Avulavirus |
| 2 | Avulavirus Infections |
| 2 | Asymptomatic Diseases |
| 2 | Air Pollution |
| 2 | Air Pollutants |
| 1 | Yellow Fever |
| 1 | Yellow Fever Vaccine |
| 1 | World War I |
| 1 | World Health Organization |
| 1 | Workforce |
| 1 | Women, Working |
| 1 | Women's Health |
| 1 | West Nile virus |
| 1 | West Nile Fever |
| 1 | Weather |
| 1 | Weaning |
| 1 | Wavelet Analysis |
| 1 | Volunteers |
| 1 | Virus Shedding |
| 1 | Virus Replication |
| 1 | Virulence |
| 1 | Virology |
| 1 | Viral Vaccines |
| 1 | Viral Plaque Assay |
| 1 | Viral Matrix Proteins |
| 1 | Viral Envelope Proteins |
| 1 | Victoria |
| 1 | Venezuela |
| 1 | Vaccines, Attenuated |
| 1 | Vaccination Refusal |
| 1 | Uterus |
| 1 | Urinary Tract Infections |
| 1 | Urban Health |
| 1 | Universities |
| 1 | Typhoid Fever |
| 1 | Turkey |
| 1 | Tumor Necrosis Factor-alpha |
| 1 | Tuberculosis |
| 1 | Tuberculosis, Pulmonary |
| 1 | Tropical Medicine |
| 1 | Transportation of Patients |
| 1 | Transplant Recipients |
| 1 | Transition Temperature |
| 1 | Transformation, Bacterial |
| 1 | Toxoplasma |
| 1 | Topography, Medical |
| 1 | Ticks |
| 1 | Third-Party Consent |
| 1 | Thimerosal |
| 1 | Thailand |
| 1 | Tetanus |
| 1 | Telephone |
| 1 | Telemedicine |
| 1 | Technology, Pharmaceutical |
| 1 | Technology Transfer |
| 1 | Taiwan |
| 1 | Tacrolimus |
| 1 | Tachypnea |
| 1 | Syphilis |
| 1 | Syndrome |
| 1 | Sympatry |
| 1 | Sunlight |
| 1 | Substance Abuse, Intravenous |
| 1 | Students |
| 1 | Structure-Activity Relationship |
| 1 | Stochastic Processes |
| 1 | Sputum |
| 1 | Sports |
| 1 | Spirometry |
| 1 | Spinal Cord Diseases |
| 1 | Spheniscidae |
| 1 | Species Specificity |
| 1 | Societies, Medical |
| 1 | Social Support |
| 1 | Social Perception |
| 1 | Social Media |
| 1 | Social Conditions |
| 1 | Social Class |
| 1 | Smoking |
| 1 | Smartphone |
| 1 | Skin Tests |
| 1 | Sirolimus |
| 1 | Singapore |
| 1 | Sick Leave |
| 1 | Sialyltransferases |
| 1 | Shock, Septic |
| 1 | Sexual Behavior |
| 1 | Sex Characteristics |
| 1 | Sequence Analysis, RNA |
| 1 | Self Medication |
| 1 | Scotland |
| 1 | Schools |
| 1 | Schizophrenia |
| 1 | Russia |
| 1 | Risk Reduction Behavior |
| 1 | Rhabdomyolysis |
| 1 | Respirovirus Infections |
| 1 | Respiratory Insufficiency |
| 1 | Respiratory Hypersensitivity |
| 1 | Residence Characteristics |
| 1 | Research Design |
| 1 | Renal Insufficiency |
| 1 | Renal Dialysis |
| 1 | Religion |
| 1 | Reference Values |
| 1 | Recombinant Proteins |
| 1 | Reassortant Viruses |
| 1 | Reagent Kits, Diagnostic |
| 1 | Rats |
| 1 | Rats, Wistar |
| 1 | Randomized Controlled Trials as Topic |
| 1 | Radiography |
| 1 | Radiography, Thoracic |
| 1 | RNA |
| 1 | RNA Viruses |
| 1 | RNA Virus Infections |
| 1 | Quality Indicators, Health Care |
| 1 | Quality Control |
| 1 | Qualitative Research |
| 1 | Q Fever |
| 1 | Pulmonary Disease, Chronic Obstructive |
| 1 | Publishing |
| 1 | Public Sector |
| 1 | Public Policy |
| 1 | Public Opinion |
| 1 | Psychosocial Deprivation |
| 1 | Prostatic Neoplasms |
| 1 | Principal Component Analysis |
| 1 | Primary Health Care |
| 1 | Primary Cell Culture |
| 1 | Preventive Medicine |
| 1 | Preservatives, Pharmaceutical |
| 1 | Prenatal Exposure Delayed Effects |
| 1 | Pregnancy Trimester, Third |
| 1 | Pregnancy Complications |
| 1 | Predictive Value of Tests |
| 1 | Precursor Cell Lymphoblastic Leukemia-Lymphoma |
| 1 | Practice Guidelines as Topic |
| 1 | Poverty |
| 1 | Poverty Areas |
| 1 | Porcine respiratory and reproductive syndrome virus |
| 1 | Polysomnography |
| 1 | Polymorphism, Restriction Fragment Length |
