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Brucellosis: Complete Clinical Approach to a Zoonotic Intracellular Infection Clinical Medicine Year 3 • diagnosis, focal disease, treatment and One Health prevention Laboratory safety: Tell the laboratory when brucellosis is suspected. Brucella can be aerosolised during processing and is a recognised laboratory-acquired infection. Handle cultures using appropriate biosafety procedures and involve public-health/veterinary services. Why brucellosis is easy to miss Brucellosis may be an acute febrile illness, an undulating fever lasting months, or a focal infection of the spine, sacroiliac joint, testis, brain or heart. It often resembles malaria, tuberculosis, enteric fever, endocarditis or inflammatory rheumatologic disease. A precise animal, food and occupational history is often the diagnostic turning point. Learning outcomes Identify the medically important Brucella species, reservoirs, routes of transmission and occupational risks. Explain intracellular survival, reticuloendothelial dissemination and focal complications. Recognise acute, subacute, chronic, relapsing and localised disease. Select blood cultures, serology, PCR and site-specific specimens while protecting laboratory staff. Construct combination treatment plans for uncomplicated and focal disease, including pregnancy and children. Prevent infection through pasteurisation, protective equipment, animal control, safe abortion-material disposal and One Health collaboration. 1. Definition and causative species Brucellosis is a zoonotic infection caused by small, gram-negative, non-motile, non-spore-forming coccobacilli of the genus Brucella. The bacteria are facultative intracellular organisms that survive within macrophages and cause prolonged bacteraemia and granulomatous inflammation. Species Main animal reservoir Human exposure pattern B. melitensis Goats and sheep Unpasteurised dairy, small-ruminant births; often severe human disease B. abortus Cattle and buffalo Raw milk, abattoir and veterinary exposure B. suis Pigs and wild swine Hunters, butchers, pig farmers; abscesses and focal disease B. canis Dogs Breeders, kennel workers and contact with reproductive material Other species Marine mammals and wildlife Rare, occupational or travel-associated disease 2. Reservoirs and transmission 2.1 Food-borne transmission Unpasteurised milk, fresh cheese, yoghurt, ice cream and other dairy products can contain organisms. Meat is a less efficient route when thoroughly cooked, but handling raw meat or organs can inoculate broken skin. 2.2 Occupational and environmental exposure Farmers, herders, veterinarians, animal-health workers, abattoir staff, butchers, slaughterhouse cleaners, laboratory workers, hunters and people assisting animal births have the highest risk. Placenta, aborted fetuses, lochia, vaginal secretions, milk and contaminated bedding may contain large numbers of bacteria. Aerosols can be generated in slaughter, necropsy, laboratory culture or cleaning. 2.3 Person-to-person transmission Human transmission is uncommon, but has been reported through breastfeeding, sexual contact, blood transfusion, tissue transplantation and perinatal exposure. A patient with brucellosis does not usually require respiratory isolation, but standard precautions and safe handling of blood/secretions are essential. 3. Pathogenesis and immunology Brucella enters through the gastrointestinal tract, conjunctiva, respiratory tract or skin breaks. It is taken up by macrophages and uses intracellular trafficking and stress-response mechanisms to avoid killing. It travels to lymph nodes, liver, spleen, bone marrow and reproductive organs. Cell-mediated immunity forms granulomas and may suppress but not eradicate the organism. Bacteraemic phase: fever, chills, sweats, malaise and hepatosplenomegaly. Reticuloendothelial persistence: organisms survive in macrophages, producing prolonged or relapsing fever. Focal seeding: bacteria localise in osteoarticular tissues, testes, CNS, heart valves, liver, spleen and lungs. Relapse: incomplete therapy, inadequate tissue penetration, undrained abscess or an unrecognised focus permits recurrence. 4. Clinical forms 4.1 Acute brucellosis Sudden or gradual fever, chills, drenching sweats, severe fatigue, headache, anorexia, myalgia and arthralgia may follow exposure. The fever can rise and fall (“undulant fever”), but this classic pattern is not required. 4.2 Subacute and chronic disease Patients may complain of months of fatigue, insomnia, irritability, poor concentration, low back pain, depression, weight loss and intermittent fever. Chronic disease can be disabling even when inflammatory markers are modest. 4.3 Osteoarticular brucellosis Sacroiliitis, spondylitis, vertebral osteomyelitis, peripheral septic arthritis and bursitis are the commonest focal complications. Back pain, hip/buttock pain, restricted movement, night pain, radiculopathy or weakness warrants MRI or specialist imaging. A painful joint requires aspiration to distinguish Brucella, pyogenic infection, TB and crystal disease. 4.4 Genitourinary disease Epididymo-orchitis, testicular pain/swelling, prostatitis, infertility and pelvic inflammatory symptoms occur through direct or haematogenous seeding. Testicular torsion must be excluded urgently in acute scrotal pain. 4.5 Neurobrucellosis Headache, meningism, confusion, cranial-nerve palsy, hearing loss, seizures, focal deficits, myelitis or psychiatric change may occur. CSF often shows lymphocytic inflammation and raised protein, but results can be atypical. Treatment is longer and requires agents with CNS penetration. 4.6 Endocarditis Endocarditis is uncommon but accounts for a disproportionate number of deaths. Persistent bacteraemia, new murmur, heart failure, embolic stroke, splenic infarct or glomerulonephritis should prompt transthoracic and often transoesophageal echocardiography. 4.7 Hepatosplenic and pulmonary disease Hepatitis, cholestasis, splenomegaly, hepatic/splenic abscesses, pneumonia and pleural disease are less common but important in severe infection. 4.8 Pregnancy and neonatal disease Brucellosis in pregnancy has been associated with miscarriage, preterm birth, intrauterine infection and neonatal disease. Review unpasteurised dairy and animal-birth exposure, involve obstetrics and do not rely on a single negative test. Urgent referral: new murmur/heart failure, neurological signs, severe back pain or weakness, acute scrotum, septic arthritis, shock, jaundice, splenic tenderness or pregnancy with systemic illness. 5. History and examination 5.1 Essential questions Which animals are kept, slaughtered, hunted or handled? Are goats, sheep, cattle, pigs or dogs involved? Was there contact with abortions, placenta, blood, milk, birthing fluid, carcasses or animal vaccination? Does the patient drink raw milk, eat fresh cheese or handle unpasteurised dairy? What is the occupation of the patient and household members? Any similar illness? Travel to pastoral, livestock or known endemic areas; previous brucellosis; incomplete antibiotic courses. Back/joint pain, testicular symptoms, headache, hearing/vision changes, cardiac symptoms, weight loss and night sweats. 5.2 Examination Measure fever, pulse, blood pressure, weight and mental state. Examine lymph nodes, liver, spleen, spine, sacroiliac joints, peripheral joints, skin, testes, heart (murmur/heart failure), lungs and neurological function. Look for focal tenderness rather than waiting for obvious abscesses. 6. Diagnosis 6.1 Blood culture Collect adequate blood cultures before antibiotics and warn the laboratory. Cultures may be negative after treatment or in chronic disease and may require prolonged incubation. A negative culture does not exclude brucellosis when exposure

Enteric Fever (Typhoid and Paratyphoid): Complete Clinical Diagnosis and Management Clinical Medicine Year 3 • systemic Salmonella infection, complications and prevention Clinical safety note: Use current Uganda Clinical Guidelines, the local antibiogram and culture susceptibility results when selecting antibiotics. Resistance patterns change; the antibiotic examples below are teaching principles and must not replace a current prescription protocol. Why enteric fever deserves more than a “typhoid” summary Enteric fever is a bloodstream and reticuloendothelial infection caused by human-adapted Salmonella. It can begin as an apparently mild prolonged fever, then produce intestinal ulceration, gastrointestinal haemorrhage, ileal perforation, encephalopathy, myocarditis, hepatitis, shock or chronic gallbladder carriage. The clinical pattern is modified by early antibiotics, malnutrition, HIV, age and antimicrobial resistance. The doctor’s task is to combine a careful exposure history, repeated examination, appropriate cultures, malaria and sepsis assessment, early fluids, resistance-aware antimicrobial treatment and surveillance for complications—especially after the first week of illness. Learning outcomes Define typhoid and paratyphoid fever and distinguish enteric fever from acute gastroenteritis. Describe Salmonella antigens, reservoirs, faecal–oral transmission and the pathogenesis of bacteraemia. Explain the clinical evolution through incubation, week one, week two, week three, relapse and carrier state. Take a relevant history and identify dehydration, sepsis, intestinal bleeding, perforation and encephalopathy. Interpret blood/stool/urine culture, susceptibility, full blood count, imaging and the limitations of Widal testing. Manage uncomplicated, severe, resistant, paediatric and pregnancy-associated disease and arrange surgical review when needed. Prevent outbreaks through water, sanitation, food safety, vaccination, case notification and carrier control. 1. Definition and terminology Enteric fever is a systemic febrile illness caused by Salmonella enterica serovar Typhi (typhoid fever) or serovars Paratyphi A, B or C (paratyphoid fever). It is different from non-typhoidal Salmonella gastroenteritis, which usually causes acute diarrhoea after contaminated food and does not follow the same prolonged bacteraemic course. Typhoid means disease caused by S. Typhi; paratyphoid is caused by S. Paratyphi. Clinically they overlap, and laboratory identification is needed to distinguish them. Humans are the major reservoir for both. 2. Organism and microbiology Salmonella enterica is a motile, facultative anaerobic, gram-negative bacillus in the Enterobacterales. Important surface structures include: O (somatic) antigen: part of the lipopolysaccharide cell wall; contributes to endotoxin activity and serological reactions. H (flagellar) antigen: associated with motility and antibody responses. Vi capsular antigen: particularly associated with S. Typhi, helping evade phagocytosis and complement. The Vi antigen is also the basis of typhoid conjugate vaccines. Intracellular survival: organisms can persist in macrophages and the gallbladder, allowing relapse and chronic carriage. Antimicrobial resistance may involve multidrug resistance, reduced fluoroquinolone susceptibility, extended-spectrum beta-lactamase production and extensively drug-resistant strains. Therefore, a historical “typhoid drug” is not automatically an appropriate modern treatment. 3. Epidemiology and transmission The supplied teaching deck emphasises contaminated water and food, houseflies, overcrowding, poor personal hygiene, poverty, inadequate sanitation and open defecation. Enteric fever spreads by the faecal–oral route when organisms from an infected person or carrier reach another person’s food or water. Risk setting/exposure Why risk rises Questions to ask Unsafe water Human sewage contaminates wells, springs, taps or storage containers Source, boiling/chlorination, recent water interruption Street/uncooked food Food handled after cooking or washed with contaminated water Raw vegetables, ice, milk, shellfish, vendors Household case Shared toilets, hands, food and towels Anyone with prolonged fever/diarrhoea or recent treatment? Institutional outbreak Schools, barracks, prisons, hospitals and crowded settlements amplify exposure Other students/workers affected? Chronic carrier Gallbladder colonisation causes intermittent stool shedding Food-handler occupation, recurrent family clusters Travel and resistance Imported strains may have different resistance patterns Recent travel, treatment abroad or previous antibiotics 4. Pathogenesis: why fever becomes systemic 4.1 Ingestion and intestinal invasion After ingestion, organisms must survive gastric acid. They reach the terminal ileum, attach to M cells over Peyer patches and cross the intestinal epithelium. Macrophages ingest them, but the bacteria survive and replicate inside the mononuclear phagocyte system. 4.2 Lymphatic and primary bacteraemia Organisms pass through mesenteric lymphatics to regional nodes and then the bloodstream. The early bacteraemia may be clinically silent and blood cultures can be negative. The liver, spleen, bone marrow and gallbladder become important sites of intracellular multiplication. 4.3 Secondary bacteraemia and clinical illness After replication in reticuloendothelial organs, organisms re-enter the bloodstream in larger numbers. Endotoxin and inflammatory mediators produce sustained fever, malaise, relative bradycardia in some patients and organ dysfunction. Organisms return to the intestine through bile, where Peyer patches become swollen, necrotic and ulcerated. 4.4 The ileal ulcer Longitudinal ulcers in the terminal ileum can erode vessels and cause haemorrhage. Full-thickness necrosis can perforate the bowel, releasing intestinal contents and causing peritonitis, sepsis and shock. The risk rises in untreated or late-presenting disease, often during the second or third week. 4.5 Relapse and carrier state Relapse may occur after apparent recovery, usually within weeks, and is often shorter and milder. Persistent organisms in the gallbladder—especially with gallstones—can lead to chronic carriage and faecal shedding without symptoms. 5. Incubation and clinical evolution Incubation is commonly 6–30 days but varies with inoculum, gastric acidity, immunity and previous vaccination. Antibiotics can blur the classical sequence. Week one: insidious onset Gradually increasing fever, malaise, headache, anorexia, dry cough and vague abdominal discomfort. Weakness, myalgia, sore throat or constipation may precede diarrhoea. The “step-ladder” fever pattern is a teaching classic, not a requirement. Week two: established systemic disease Persistent high fever, toxic appearance, coated tongue with a relatively clean tip, abdominal tenderness, diarrhoea or constipation. Relative bradycardia can occur but is neither sensitive nor specific. Hepatosplenomegaly and faint salmon-coloured rose spots on the trunk may appear; absence does not exclude disease. Apathy, confusion, delirium or a “typhoid state” suggests encephalopathy and severe illness. Week three: complications Untreated patients may develop intestinal bleeding, perforation, peritonitis, encephalopathy, myocarditis, hepatitis, pneumonia, renal injury, shock or disseminated intravascular coagulation. Recovery, relapse and prolonged fatigue Fever and systemic symptoms may abate over two to four weeks after effective therapy, but lethargy, weight loss and reduced concentration can persist. Relapse resembles the original illness but is commonly shorter. Persistent fever must trigger a search for resistance, a complication

Tuberculosis (TB): A Complete Clinical Guide to Pathogenesis, Diagnosis, Treatment and Prevention Clinical Medicine Year 3 • Uganda-focused, student-doctor teaching chapter Clinical safety note: This chapter is for learning and clinical reasoning. Anti-tuberculosis regimens, doses, HIV timing, preventive therapy and drug-resistant TB combinations must be checked against the current Uganda Clinical Guidelines, Uganda National TB and Leprosy Programme (NTLP) protocols, the patient’s weight, susceptibility result, pregnancy status, organ function and drug-interaction profile. Why tuberculosis deserves a full chapter Tuberculosis is not only a respiratory illness. It is a dynamic interaction between an inhaled organism, the host immune response, social conditions and the health system. A patient may have contagious cavitary pulmonary disease, a small lymph-node lesion, tuberculous meningitis, spinal cord compression, disseminated miliary disease or post-TB lung damage. The same patient may also have HIV, diabetes, malnutrition, pregnancy, renal disease or previous treatment that changes the presentation and the safest regimen. The essential clinical job is therefore broader than “give six months of tablets.” The clinician must find infectious cases early, collect the right specimen before antibiotics when possible, interpret a negative test in context, identify rifampicin resistance, assess HIV and comorbidities, start the correct regimen, support adherence, monitor toxicity, screen contacts and document the treatment outcome. Learning outcomes Define TB disease, latent TB infection, pulmonary TB, extrapulmonary TB and drug-resistant TB. Describe the microbiology of Mycobacterium tuberculosis, its transmission and its survival within macrophages. Explain the formation of the Ghon focus, primary complex, granuloma, caseation, cavitation, latency and reactivation. Recognise the clinical features of pulmonary, pleural, lymph-node, CNS, spinal, abdominal, genitourinary, pericardial, miliary and congenital/childhood TB. Take a complete TB history and perform a focused examination, including red-flag assessment. Select sputum, extrapulmonary and childhood specimens; interpret molecular tests, smear, culture, chest imaging, LF-LAM, TST/IGRA and susceptibility testing. Construct a safe management plan for drug-susceptible TB, TB/HIV, children, pregnancy, TB meningitis/pericarditis and drug-resistant TB. Recognise adverse effects, treatment failure, relapse, complications, post-TB lung disease and infection-control needs. Plan contact investigation, TB preventive treatment, vaccination, adherence support and public-health follow-up. 1. Definition and important distinctions Tuberculosis disease is illness caused by active multiplication of organisms in a person’s tissues, with symptoms, signs, microbiological evidence, imaging abnormalities or a combination of these. It can affect any organ. Latent TB infection (LTBI) means viable bacilli are contained by the immune system without clinical disease. The person has no symptoms caused by TB and does not ordinarily transmit infection, but can develop disease later if immune control weakens. Infectious TB usually refers to untreated pulmonary or laryngeal disease in which bacilli are aerosolised. Most isolated extrapulmonary disease is not transmitted person-to-person, although pulmonary involvement must be excluded. TB/HIV co-infection means both infections are present. HIV changes the probability of progression, the radiological pattern, the frequency of extrapulmonary disease, the interpretation of tests and the timing/choice of antiretroviral therapy. 2. Causative organism and microbiology 2.1 The tubercle bacillus Mycobacterium tuberculosis is a slender, aerobic, non-motile, non-spore-forming bacillus. Its lipid-rich mycolic-acid cell wall makes it “acid-fast”: once stained, it resists decolourisation by acid-alcohol. The organism grows slowly, prefers oxygen-rich tissues and can survive for years in a dormant state inside granulomas. Acid-fastness: useful for smear microscopy, but a smear shows acid-fast bacilli and cannot by itself prove that every bacillus is M. tuberculosis. Slow growth: explains why culture and some susceptibility tests take longer than molecular tests. Intracellular survival: prevents easy killing by macrophages and permits persistence in a low-metabolic state. Lipid cell wall: contributes to resistance to environmental stress and affects drug penetration. Complex rather than single species: M. tuberculosis complex includes M. bovis and related organisms; this matters for zoonotic exposure and pyrazinamide susceptibility. 2.2 Why the organism is difficult to eradicate Within one patient, bacilli may occupy different biological environments: rapidly multiplying organisms in cavities, slowly multiplying organisms in acidic necrotic tissue and dormant bacilli within granulomas. Combination therapy is required so that resistant mutants are suppressed and organisms in different compartments are treated. Poor adherence, inadequate absorption, drug interactions or an incorrect regimen can select drug resistance. 3. Epidemiology and determinants of disease The linked Uganda teaching resource describes TB as a continuing public-health emergency and highlights the current national strategy’s emphasis on rapid molecular diagnosis, shorter regimens, decentralised care and digital adherence monitoring. It identifies a high burden of TB/HIV co-infection, childhood TB and drug-resistant TB. WHO updates burden estimates annually, so students should use the latest report rather than memorising an old global number. Read the Uganda TB teaching resource. Determinant How it increases risk Clinical implication HIV infection Loss of CD4-mediated containment; rapid progression and disseminated disease Test every presumptive/diagnosed patient; look for extrapulmonary TB and opportunistic illness Young children Immature immunity and inability to expectorate sputum Household contact tracing, stool/gastric aspirate and clinical diagnosis may be needed Diabetes Impaired cellular immunity and altered pharmacokinetics Screen, optimise glucose and monitor treatment response Undernutrition Weakens immune responses and worsens drug toxicity Nutrition assessment, supplementation and weight-band dose review Silicosis/mining Damaged macrophage function and high occupational exposure Ask about mining/quarry work and screen actively Prisons, slums, refugee settlements Crowding, poor ventilation and delayed diagnosis Active case finding, ventilation, rapid isolation and contact investigation Smoking and alcohol Impaired mucociliary clearance, immunity and adherence Brief intervention and adherence support Immunosuppressive treatment Loss of granuloma integrity Screen before biologics/high-dose steroids and investigate new symptoms urgently Previous TB therapy Raises probability of acquired resistance or relapse Obtain old records and perform rapid resistance testing 4. Transmission and infection-control reasoning 4.1 How transmission occurs When a person with infectious pulmonary or laryngeal TB coughs, speaks, sings or undergoes an aerosol-generating procedure, tiny droplet nuclei containing bacilli remain suspended in air. Transmission is more likely indoors, in crowded rooms, in poor ventilation and after prolonged exposure. A brief outdoor encounter is generally much less risky than sharing a poorly ventilated sleeping room. Infection is not normally acquired from handshakes, sharing plates or touching intact skin. However, respiratory secretions and contaminated tissues still require standard infection-control precautions.

DCM 3101 • LWA 1 • Sub-topic 1.2 Factors influencing disease transmission and control Transmission is the movement of an infectious agent from a reservoir or source to a susceptible host. Control means reducing incidence, prevalence, complications and transmission; elimination and eradication are more ambitious endpoints. A clinician controls disease at the bedside and through the health system by identifying the active link in the transmission cycle. Learning outcomes Explain the epidemiological triad of agent, host and environment. Identify predisposing factors that increase acquisition or severe disease. Distinguish contact, droplet, airborne, food-borne, water-borne, blood-borne, sexual, vertical and vector transmission. Apply the chain of infection to a patient, household and health-care outbreak. Select primary, secondary and tertiary control measures and evaluate their limitations. 1. The epidemiological triad Disease patterns emerge from interaction among the agent, the host and the environment. A wet climate may increase mosquito habitat; human drainage may reduce stagnant water; altitude and temperature may alter agent survival or vector development. When the interaction remains relatively stable, disease may be endemic. When one component changes, transmission can increase or collapse. Component Factors Clinical and public-health question Agent Infective dose, survival, virulence, invasiveness, toxin production, antigenic change and antimicrobial resistance. How much exposure is required, how long does it survive, and can treatment reduce shedding? Host Age, sex, pregnancy, immunity, vaccination, nutrition, genetics, comorbidities, behaviour and access to care. Who is susceptible, who is infectious, and who needs prophylaxis or priority protection? Environment Climate, season, housing, crowding, sanitation, water, food, vectors, occupation, travel, conflict and health-care systems. What conditions allow persistence and which environmental change would interrupt transmission? 2. Predisposing factors Factor How it increases transmission or disease Examples Poor environmental sanitation Allows faecal contamination, vectors and unsafe waste disposal. Polluted water, open defecation, blocked drains, poor air quality. Poor personal hygiene Increases hand, fomite, food and contact transmission. Infrequent handwashing, unsafe food handling, shared personal items. Crowding and displacement Increases close contact, reduces isolation and disrupts health services. Refugee settlements, prisons, dormitories, mass gatherings. Substance use and risky behaviour May damage immunity, increase exposure or reduce adherence to prevention. Smoking, harmful alcohol use, unsafe injections, unprotected sex. Low vaccination and limited health access Leaves susceptible hosts and delays diagnosis, treatment and contact tracing. Missed immunisation, transport barriers, medicine stock-outs. Climate and geography Changes vector density, water safety, agent survival and population movement. Floods, drought, warm humid climates, forests and stagnant water. Host vulnerability Weakens barriers or immune responses. Infancy, old age, pregnancy, malnutrition, diabetes, HIV and immunosuppression. Socio-economic conditions Shape housing, nutrition, occupation, sanitation and ability to seek care. Poverty, overcrowded housing, hazardous work and food insecurity. 3. Modes of transmission Mode How it occurs Control examples Direct contact Infectious blood, body substances, skin or mucosa contact another person or animal directly. Gloves when indicated, wound covering, condoms, hand hygiene and safe sharps. Indirect contact Hands, surfaces, utensils, linen, phones, keyboards, taps or instruments pass organisms. Cleaning, disinfection, sterilisation, equipment separation and hand hygiene. Droplet Larger respiratory particles from cough, sneeze, talk or splash reach nearby mucosa. Source control, masks, distance, ventilation and respiratory etiquette. Airborne Small aerosols or droplet nuclei remain suspended and are inhaled over distance or time. Ventilation, respirators, appropriate isolation and reduced crowding. Food-borne Consumption of contaminated or inadequately cooked food. Safe preparation, temperature control, hand hygiene and inspection. Water-borne Consumption or use of contaminated water. Safe water, chlorination, protected wells, sanitation and outbreak response. Vector-borne A mosquito, tick, tsetse fly or other vector carries the agent biologically or mechanically. Bed nets, repellents, indoor spraying, drainage, protective clothing and case treatment. Blood-borne and sexual Blood, semen, vaginal fluid or other infectious material enters tissue or mucosa. Condoms, testing, safe injections, screened blood, PrEP/PEP where indicated. Vertical Mother-to-child transmission during pregnancy, delivery or breastfeeding. Antenatal testing, maternal treatment, safe delivery and infant prophylaxis. 4. The disease-transmission cycle The cycle links pathogen, reservoir, portal of exit, mode of transmission, portal of entry and susceptible host. A respiratory pathogen may leave through the nose, travel in droplets, enter another person’s airway and establish infection. A diarrhoeal pathogen may leave in stool, contaminate water or food, enter through the mouth and multiply in the intestine. The same principle guides both clinical precautions and community control. Break the link Agent: effective treatment, sterilisation and disinfection. Reservoir: diagnose, treat, isolate, clean the environment and manage animal sources. Portal of exit: masks, cough etiquette, wound covering, safe toilets and sharps safety. Transmission: hand hygiene, PPE, ventilation, food and water safety, vector control. Portal of entry: vaccination, barrier methods, aseptic technique and protective equipment. Susceptible host: vaccination, prophylaxis, nutrition, chronic-disease control and early care. 5. Airborne and droplet transmission in practice Droplets can deposit on the eyes, nose or mouth after sneezing, coughing, talking or splashes. Airborne aerosols remain suspended longer and may be inhaled in poorly ventilated spaces. The distinction is not merely a label: it determines room ventilation, distance, mask or respirator selection, patient placement and duration of precautions. Influenza, mumps, rubella and meningococcal disease illustrate droplet risk; tuberculosis and measles require airborne thinking. 6. Contact transmission and fomites Direct contact occurs when infectious material reaches another person through skin, mucosa, wounds or sexual contact. Indirect contact occurs through inanimate objects such as phones, keyboards, taps, linen, utensils or poorly processed instruments. Health-care workers can become a bridge between patients; hand hygiene at the correct moments and cleaning of shared equipment are high-value interventions. 7. Control and prevention Level Purpose Examples Primary prevention Prevent exposure or initial infection. Vaccination, safe water, sanitation, condoms, vector control, ventilation, nutrition and hand hygiene. Secondary prevention Detect early disease and interrupt further spread. Screening, testing, contact tracing, isolation, notification, prophylaxis and prompt treatment. Tertiary prevention Reduce complications, disability, relapse and onward transmission from chronic disease. Rehabilitation, adherence support, chronic infection care and prevention of organ damage. Control programme Reduce incidence, prevalence or impact to a planned level. Surveillance, case management, vaccination campaigns and quality improvement. Elimination Reduce transmission to zero in a defined geographic