Pathogens: germs, infection types, and field decisions

Without a laboratory, you cannot confirm whether a sick person has a bacterial infection, a virus, a fungal overgrowth, or a parasite. But decisions still have to be made — whether to isolate, whether to start an antibiotic, whether to focus on rehydration, or whether to evacuate. This page is the mental model that makes those decisions rational rather than guesswork. Every syndrome page in this medical library — diarrhea, respiratory infections, wound infections, skin fungus, urinary infections, fever — routes back here for the underlying framework.

Educational use only

This page provides general educational information for emergency preparedness scenarios when professional medical care is unavailable. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider. Use this information at your own risk.

Action block

Do this first: Print this page and the field hygiene page and store them with your medical kit (active time: 15 minutes). Time required: Active: 15 min to print and file; ongoing reference use. Cost range: Inexpensive (paper and ink only). Skill level: Beginner to intermediate — no clinical training required to use the decision framework. Tools and supplies: Printer, paper, waterproof bag or lamination sleeve for field storage. Antibiotic stockpile per medical stockpiling. Safety warnings: See Antibiotics do not treat viruses below — using the wrong medicine class can cause serious harm.

The five pathogen classes

Every infectious disease is caused by one of six categories of organism. Knowing the category tells you what medicines work, how the pathogen spreads, and how the body responds. (Ectoparasites are included in the table below as a sixth practical category, though they are technically not pathogens in the microbiology sense.)

Organism class What it is How it reproduces Typical illness pattern What kills or controls it What does NOT work
Bacteria Single-celled living organism with its own metabolism Divides by binary fission; doubles every 20–30 minutes in ideal conditions Skin infections, pneumonia, urinary infections, sepsis, foodborne illness; fever common Antibiotics (class-specific); antiseptics on skin Antivirals; antifungals; most antiparasitics
Viruses Protein shell containing DNA or RNA; not alive independently Hijacks host cells to replicate; spread is rapid within a host Respiratory illness, gastroenteritis, rashes, hepatitis; self-limiting in most healthy hosts Immune system (primary); specific antivirals for a narrow set (influenza, herpes, HIV, hepatitis B/C) Antibiotics (no effect on viruses); antifungals
Fungi Eukaryotic organisms; mold and yeast forms Spores and budding; grow in warm, moist environments Skin/nail infections, vaginal yeast, thrush, lung infections in immunocompromised hosts Antifungals (topical or oral, organism-specific); improved skin dryness for superficial infections Antibiotics (no effect); antivirals (no effect)
Protozoa Single-celled parasites with complex lifecycle Often require an intermediate host or vector; cysts survive outside the host Diarrhea (Giardia, Cryptosporidium, amoeba), malaria, toxoplasmosis Antiprotozoal drugs (metronidazole, tinidazole, nitazoxanide, chloroquine — organism-specific) Standard antibiotics (incomplete or no effect); antivirals; antifungals
Helminths Multicellular worms — roundworms, tapeworms, flukes Eggs or larvae shed in feces or intermediate host; adult worms can live years in the gut Abdominal pain, malnutrition, anemia, visible worms in stool; often asymptomatic for months Antihelmintic drugs (albendazole, mebendazole, praziquantel — organism-specific) Antibiotics; antivirals; antifungals; antiprotozoals (different mechanism)
Ectoparasites Arthropods living on or in skin — lice, scabies mites, ticks, fleas Reproduce on or in the host; spread by direct skin contact or shared bedding/clothing Intense itch, visible insects or tracks, secondary skin infection from scratching Permethrin (topical, kills on contact); oral ivermectin for scabies; pediculicides for lice; mechanical removal for ticks Internal antibiotics (treat secondary infection only, not the parasite itself)

Sources: CDC About Parasites (updated November 2024); NCBI Bookshelf — How Infection Works; WHO Antimicrobial Resistance Fact Sheet.

What medicines work against what

The most important rule in field medicine is also the one most commonly broken: each medicine class works against a specific organism class, and not against the others. Using the wrong class provides no benefit and carries real risk — side effects, gut disruption, and contribution to resistance.

Antibiotics — bacteria only

Antibiotics kill or inhibit bacteria by targeting structures that bacteria have and human cells do not: cell walls, ribosomes, and DNA replication enzymes. They have zero mechanism of action against viruses, fungi, protozoa, or helminths.

Commonly stockpiled antibiotics and their primary targets:

Antibiotic Class Primary uses in a field setting Notes
Cephalexin (Keflex) Cephalosporin Skin and soft tissue infections, non-purulent cellulitis, mild respiratory infections Does not cover MRSA
Amoxicillin Penicillin Ear/sinus infections, strep throat, dental infections, mild respiratory infections Does not cover MRSA; avoid if penicillin-allergic
Doxycycline Tetracycline Tick-borne illness (Lyme, Rocky Mountain Spotted Fever), pneumonia, MRSA-risk skin infections, malaria prophylaxis Not for children under 8 or pregnant women; reduces oral contraceptive reliability
TMP-SMX (Bactrim) Sulfonamide/trimethoprim MRSA-risk skin infections and abscesses, urinary infections, some respiratory infections High sulfa allergy rate; check before stockpiling; 98% sensitivity against community-acquired MRSA
Metronidazole (Flagyl) Nitroimidazole Anaerobic bacterial infections (abdominal, dental), also active against Giardia and amoeba Dual antibacterial and antiprotozoal; no alcohol during treatment
Clindamycin Lincosamide Skin and soft tissue, dental infections, MRSA alternative; penicillin-allergy patients Risk of C. difficile colitis — use only when indicated
Azithromycin Macrolide Respiratory infections, traveler's diarrhea (bacterial), STIs Resistance is rising in many respiratory pathogens; cardiac QTc risk at high doses

Antibiotics do not treat viruses

Using antibiotics for a cold, flu, or stomach bug caused by a virus provides no clinical benefit and causes real harm: disruption of gut flora, increased risk of Clostridium difficile colitis, allergic reactions, and contribution to community antibiotic resistance. Resistance is how we end up with infections that no medicine can treat. This is not a theoretical concern — the WHO 2024 Bacterial Priority Pathogens List identifies 15 families of drug-resistant bacteria already posing critical or high global threats.

Antivirals — narrow spectrum for specific viruses

Most viral illnesses have no antiviral treatment. The immune system resolves them. Antivirals exist for a small number of viruses where early intervention meaningfully changes outcomes:

  • Oseltamivir (Tamiflu) — influenza A and B only, effective if started within 48 hours of symptom onset; reduces duration by roughly 1 day and severity in high-risk groups (CDC, ACIP)
  • Acyclovir / valacyclovir — herpes simplex (cold sores, genital herpes, chickenpox, shingles); reduces severity and duration; does not cure — virus remains latent
  • Antiretrovirals (ARTs) — HIV; lifelong suppressive therapy; not a field stockpile item but critical to not interrupt for HIV-positive household members

For the overwhelming majority of viral illnesses — common cold, norovirus, most flu strains without complication, typical viral respiratory infections — treatment is supportive: rest, hydration, fever management with acetaminophen or ibuprofen, and isolation to prevent spread.

Antifungals — fungi only

Fungi differ from bacteria in their cell structure. Most antibiotics have no effect. Antifungals target ergosterol (a component of fungal cell membranes not found in human cells or bacteria).

  • Topical options (inexpensive, no prescription in the US):
    • Clotrimazole 1% cream — athlete's foot, ringworm, jock itch
    • Terbinafine 1% cream or spray — athlete's foot, ringworm; often faster clearance than clotrimazole
    • Miconazole 2% — vaginal yeast, skin fungal infections
  • Oral options (require prescription in most settings):
    • Fluconazole 150 mg single dose — vaginal candidiasis; 7–14 days for oral thrush
    • Fluconazole 150–300 mg once weekly for 3–6+ months (fingernails 3–6 months; toenails 6–12 months) — nail fungal infection (onychomycosis); pulse dosing is the standard regimen because fluconazole concentrates in nail keratin

Topical antifungals typically require 2–4 weeks of consistent application. Stopping early because the rash looks better is the primary reason fungal infections recur. Keep the skin dry — moisture is what fungi need to persist.

Antiparasitics — organism-specific

Parasites vary enormously in biology, so antiparasitic drugs are highly specific:

  • Metronidazole or tinidazole — Giardia lamblia (standard first line in the US); also active against intestinal amoeba. Tinidazole works as a single 2 g dose vs. metronidazole 250 mg three times daily for 5–7 days (CDC Giardia clinical care guidance)
  • Nitazoxanide — Cryptosporidium (the only drug with demonstrated efficacy in immunocompetent patients) and also active against Giardia; 500 mg twice daily for 3 days in adults
  • Albendazole 400 mg or mebendazole 100 mg — roundworms, hookworms, pinworms, whipworms; albendazole also active against some tapeworms; single-dose regimens for many species
  • Praziquantel — tapeworms and flukes; single dose is usually curative
  • Permethrin 5% cream — scabies (leave on 8–14 hours, repeat in one week); also used on clothing at 0.5% concentration for tick and mosquito prevention
  • Pediculicide shampoos (permethrin 1% or pyrethrin-based) — head lice; require mechanical nit removal; follow with fine-tooth comb

Bacterial spores: a special problem

Most people understand that boiling water kills bacteria. What most people do not know — and what has killed people — is that boiling at 212°F (100°C) at sea level kills vegetative (actively growing) bacteria but does not reliably kill all bacterial spores.

Spores are the dormant survival form of certain bacteria. They have a tough protein coat and can withstand extreme heat, drying, UV radiation, and many chemical disinfectants. When conditions improve, they germinate back into active vegetative bacteria.

Clostridium botulinum: the pressure canning reason

Clostridium botulinum produces botulinum toxin — one of the most potent toxins known. The spores of C. botulinum survive standard boiling. This is precisely why the USDA National Center for Home Food Preservation requires pressure canning for all low-acid foods. Pressure canning raises the internal temperature above 240°F (116°C) — high enough to destroy the spores themselves, not just the vegetative bacteria (CDC Botulism Prevention; USDA FSIS Botulism).

Low-acid foods that require pressure canning (not water-bath canning) include: all vegetables except pickled/acidified ones, meats, poultry, fish, seafood, and low-acid sauces. See food preservation and canning for the full pressure canning procedure and processing times.

Boiling low-acid canned food does not make it safe

If low-acid food was improperly canned without a pressure canner, boiling it for 10 minutes before eating destroys the toxin but does not kill the spores — and may not fully eliminate pre-formed toxin in large jars. Prevention is the only reliable strategy. Never consume home-canned low-acid food from containers that are swollen, leaking, or smell off, regardless of how long you boil it. When in doubt, throw it out.

Other dangerous spore-forming bacteria

  • Clostridium tetani (tetanus) — spores live in soil indefinitely, especially disturbed soil, gravel, rust, and feces. Wound contamination with soil is the primary infection route. Once tetanus toxin is produced and spreads to the nervous system, there is no antidote — only prevention (tetanus vaccination) and supportive ICU care. See wound infection for tetanus vaccination decision criteria.

  • Clostridium perfringens (gas gangrene) — spore-former that produces tissue-destroying toxins under anaerobic conditions (deep wound pockets, contaminated wound closure without adequate drainage). Can also cause a rapid foodborne illness from improperly held cooked meat (the vegetative form grows at 40–140°F (4–60°C); proper hot-holding above 140°F (60°C) prevents illness from the vegetative form, but spores survive and can germinate if food cools slowly).

  • Bacillus cereus — produces a heat-stable toxin in rice and other starchy foods held at room temperature. The toxin (not the bacteria) causes vomiting within 1–5 hours. Reheating food after the toxin has formed does not destroy it. Prevention: refrigerate cooked rice within 2 hours, reheat to 165°F (74°C), never leave cooked starchy foods at room temperature for more than 2 hours.

  • Clostridioides difficile (C. diff) — a spore-former that causes severe colitis, especially after antibiotic use that disrupts normal gut flora. Three critical field facts about C. diff:

    1. Alcohol-based hand sanitizer does not inactivate C. diff spores. The CDC recommends soap-and-water handwashing when a C. diff infection is suspected or confirmed, because the physical friction of washing removes spores from skin surfaces.
    2. Environmental surfaces require disinfection with a 1:10 bleach solution (one part household bleach to nine parts water) — standard quaternary ammonium cleaners are not effective against C. diff spores.
    3. Risk is highest following use of clindamycin, fluoroquinolones, cephalosporins, and ampicillin — the same antibiotics commonly used for skin and respiratory infections. This is one more reason to use antibiotics only when indicated.

For the mechanics of C. diff transmission and the complete hand hygiene protocol, see field hygiene.

How pathogens spread in austere settings

Knowing the transmission route directly determines the prevention priority. In a disrupted infrastructure scenario, multiple transmission routes operate simultaneously.

Fecal-oral route

This is the most underestimated killer in austere conditions. Pathogens shed in feces — bacteria, viruses, protozoa, and helminth eggs — contaminate water, hands, and food. The result is diarrhea, vomiting, abdominal illness, and dehydration. Cholera, typhoid, Giardia, Cryptosporidium, hepatitis A, norovirus, and rotavirus all travel this route.

Prevention requires all three links broken simultaneously: safe water (see water boiling and water filtration), handwashing with soap after toilet use and before food preparation, and proper waste disposal away from water sources. Disrupting even one link increases disease burden significantly. See field hygiene for latrine construction and group handwashing station setup.

Respiratory route

Pathogens in airborne droplets or droplet nuclei spread when people share enclosed space — tents, shelters, vehicles, evacuation centers. Influenza, tuberculosis, COVID-19, measles, whooping cough, and streptococcal pharyngitis all use this route. Crowding, poor ventilation, and shared sleeping spaces amplify transmission dramatically.

Interventions: distance (6 feet / 1.8 m for larger droplets), N95 or equivalent respirator for high-risk care situations, ventilation with outside air, and isolation of symptomatic individuals to a separate room. For full household quarantine and isolation setup, see pandemic preparedness.

Skin and wound route

Broken skin is an open door. Soil and debris in wounds introduce bacteria (including tetanus spores and C. perfringens), and animal or human bites introduce polymicrobial bacterial loads. Secondary infection of wound sites is one of the most common causes of death from otherwise survivable injuries. Cross-reference wound care and wound infection recognition for prevention and early management.

Skin-to-skin contact also transmits ectoparasites (scabies, lice) and some fungal infections (ringworm). In group shelter settings, shared clothing, bedding, and towels become vectors.

Vector-borne route

Arthropods — ticks, mosquitoes, fleas, and lice — carry pathogens between animal reservoirs and humans. In North America the most important vectors are:

  • Ticks → Lyme disease (Borrelia burgdorferi), Rocky Mountain Spotted Fever (Rickettsia rickettsii), ehrlichiosis, anaplasmosis, tularemia
  • Mosquitoes → West Nile virus, Eastern Equine Encephalitis (EEE), dengue in warm southern regions
  • Fleas → murine typhus; historically plague (Yersinia pestis)
  • Body lice → typhus (Rickettsia prowazekii), relapsing fever (Borrelia recurrentis) — historically catastrophic in crowded, low-hygiene conditions such as refugee camps and siege situations

For tick removal and early tick-borne illness recognition, see tick bites and tick-borne illness. Lice and scabies prevention belongs in the personal hygiene section of field hygiene.

Foodborne route

Foodborne illness is distinct from fecal-oral transmission in one critical way: the pathogen or its toxin is already in the food before it is consumed. Mechanisms include:

  • Inadequate cooking temperatures: Poultry needs to reach 165°F (74°C) internal temperature; ground meat 160°F (71°C); whole-muscle beef and pork 145°F (63°C) plus a 3-minute rest. Undercooking is the most common cause of Salmonella and Campylobacter infection.
  • Improper holding temperatures: Bacterial growth occurs in the 40–140°F (4–60°C) "danger zone." Food held in this range for more than 2 hours can accumulate dangerous bacterial loads.
  • Low-acid canning failures: As described in the spore section above, improperly pressure-canned low-acid foods can harbor botulinum toxin without visible signs of spoilage.
  • Raw milk and unpasteurized products: Can carry Listeria, Salmonella, E. coli O157:H7, Campylobacter, and Cryptosporidium.
  • Cross-contamination: Raw meat juices contaminating ready-to-eat foods via shared cutting boards, hands, or utensils.

See food storage for holding temperature guidance and canning for pressure canning requirements.

Field decision box: what to do without a lab

Without diagnostic tools, the decision framework relies on syndrome recognition — the pattern of symptoms tells you which organ system is involved, which pathogen class is most likely, and what the right response is.

Field note

Step 1 — Identify the syndrome.

Look at what the patient's body is doing, not just what they say hurts.

  • Wound/skin hot, red, swollen, draining → wound infection or skin abscess. See wound infection. Use the STONES assessment.
  • Diarrhea or vomiting, no fever or low fever → likely viral gastroenteritis (most common) or foodborne toxin. Start oral rehydration immediately.
  • Diarrhea with blood or mucus, or prolonged >7 days → possible bacterial enteritis or protozoal infection (Giardia, amoeba). Requires specific treatment.
  • Respiratory: cough, congestion, sore throat → likely viral (most respiratory illness is viral). Supportive care first.
  • Respiratory: fever >103°F (39.4°C), rapid breathing >20/min, chest pain, productive green/brown sputum → possible bacterial pneumonia. May need antibiotics.
  • Skin patch, ring-shaped or scaling → likely fungal (ringworm, athlete's foot, jock itch). Start topical antifungal; do not start antibiotics.
  • Fever alone with no localizing signs in first 24–48 hours → viral syndrome most likely. Monitor for localizing symptoms before deciding on antibiotics.
  • Fever + stiff neck + headache + light sensitivity → possible meningitis. Evacuate immediately — this is a medical emergency.

Step 2 — Apply the syndrome-specific recognition framework.

  • Wound infections → STONES (Swelling, Temperature, Odor, New symptoms, Exudate, Size of redness). See wound infection.
  • GI illness → assess dehydration severity first (skin turgor, urine output, mucous membranes, mental status). See dehydration and ORS.
  • Respiratory illness → count respiratory rate (normal adult: 12–20/min). Rate ≥22/min is a warning sign for severity.
  • Skin infections → is the border spreading? Is there systemic fever? Spreading cellulitis needs antibiotics; localized folliculitis or fungal rash may not.

Step 3 — Make the treatment decision.

Choose one of these five responses, not a mix of all of them:

  1. Supportive care only — viral illness with no bacterial superinfection. Hydration, rest, fever management. No antibiotics.
  2. Topical treatment — localized skin fungus, minor wound, early ectoparasite infestation. Targeted topical agent, monitoring.
  3. Isolate the patient — symptomatic respiratory illness in a group setting. Separate room, mask on the caregiver, dedicated cup and towel, ventilation.
  4. Start oral antibiotics IF criteria met — spreading wound redness, fever above 100.4°F (38°C) with a bacterial-pattern illness, suspected urinary infection with systemic signs. Use the narrowest spectrum antibiotic that covers the likely organism.
  5. Evacuate now — qSOFA score ≥2 (altered mental status + rapid breathing ≥22/min or systolic BP ≤100 mm Hg), stiff neck with high fever, red streaks tracking toward the body core from a wound, respiratory rate ≥25/min with confusion. No field intervention is adequate as definitive treatment for sepsis, meningitis, or necrotizing soft tissue infection.

Step 4 — Reassess on schedule.

  • Sepsis-risk or spreading cellulitis → reassess every 6–12 hours.
  • Dehydration from GI illness → reassess ORS response every 4–6 hours.
  • Stable fever without localizing signs → reassess every 12–24 hours.
  • Ectoparasite or fungal treatment → reassess at 48–72 hours for early response, then weekly.

The goal of reassessment is to catch the patient who is not improving. A wound that is unchanged at 24 hours on antibiotics is reassuring. A wound that is larger at 24 hours on antibiotics is an escalation trigger.

Common mistakes that get people killed

These are not theoretical errors. They appear repeatedly in austere-environment medical literature and in disaster medicine after-action reports.

1. Treating viral illness with antibiotics. The common cold, influenza (most years), norovirus, rotavirus, and ordinary viral upper respiratory infections do not respond to antibiotics. Starting amoxicillin for a sore throat caused by a virus does nothing for the infection and disrupts the gut microbiome, increases risk of C. difficile colitis, and selects for resistant organisms in the community. The correct response to most respiratory and GI illness is hydration and supportive care, not an antibiotic.

2. Skipping ORS in diarrheal illness. "They're not that dry yet" is not a safe rationale for delaying oral rehydration solution (ORS). Dehydration kills faster than the infection itself in many diarrheal illnesses. By the time a patient looks dry — sunken eyes, tented skin, minimal urine output — they have already lost 5–8% of body weight in fluid. Start ORS at the first episode of watery diarrhea or vomiting. See dehydration and ORS for the WHO formulation and dosing by severity.

3. Misidentifying fungal infection as cellulitis (or vice versa). Athlete's foot with secondary fissuring can look like early cellulitis. Cellulitis misidentified as ringworm gets antifungal cream instead of antibiotics. The key distinguishing features: fungal infections are typically ring-shaped or scaling with clear centers, do not cause fever, and have distinct borders. Cellulitis is warm, poorly demarcated, tender, and spreads in a pattern that follows lymphatic drainage. If in doubt, treat for the more dangerous diagnosis while monitoring for signs of the other. A patient treated for cellulitis who is not improving at 48 hours should prompt a reassessment including fungal infection.

4. Relying on hand sanitizer against C. diff and norovirus. Alcohol-based hand sanitizer does not reliably inactivate Clostridioides difficile spores or norovirus (CDC Norovirus Prevention; CDC C. diff guidelines for clinicians). Both organisms require soap-and-water handwashing, which physically removes the organisms from skin rather than chemically inactivating them. In a known or suspected C. diff situation, environmental surfaces also require a 1:10 bleach solution (1 part bleach to 9 parts water), not standard disinfectants. This matters in any group shelter scenario where someone has active diarrhea.

5. Boiling water and then using it for improperly canned low-acid foods. A common field assumption: "if I boil the food before eating it, any botulism toxin will be destroyed." Boiling at 212°F (100°C) for 10 minutes destroys botulinum toxin but does not kill C. botulinum spores. Those spores can germinate and produce new toxin under the right conditions. More importantly, in practice, uniform toxin destruction in a large jar through boiling is not guaranteed. The CDC and USDA are explicit: if a low-acid food was not pressure-canned at 240°F (116°C), it should not be consumed regardless of subsequent boiling (CDC Botulism Prevention; USDA FSIS Botulism).

6. Stopping antibiotics early because the patient feels better. Antibiotics work before symptoms fully resolve. The patient feels better when the bacterial load drops below the threshold for symptoms — often 2–3 days into a 5–7 day course. Stopping there means residual bacteria survive and potentially develop resistance. The course must be completed as prescribed. The single exception: if the patient develops a severe allergic reaction (rash, swelling, throat tightening) — stop immediately and treat for allergy.

7. Sharing antibiotic stockpiles without matching syndrome to organism class. An antibiotic stockpile is not a general-purpose medicine kit. Cephalexin appropriate for a skin infection is not the right choice for a urinary infection caused by a resistant organism. TMP-SMX appropriate for a MRSA-risk skin infection is not the right choice for an anaerobic abdominal infection. Before pulling from the antibiotic supply, confirm: (a) this is a bacterial syndrome, not viral or fungal; (b) the likely organism class matches the antibiotic's spectrum; (c) the patient has no documented allergy to that class. See medical stockpiling for field antibiotic matching guidance.

Teach your family

The following rules should be known by every adult in a household before a crisis, not learned during one. They are grounded in the same biology as everything above, simplified for daily use.

1. Wash hands with soap and running water for 20 seconds. Count it out. After using the toilet, after changing diapers, before preparing food, after touching anything from outside — including packages, mail, and animals. Alcohol sanitizer is a backup when water is unavailable, not a substitute. It does not work against C. diff or norovirus.

2. Most colds and stomach bugs do not need antibiotics. Viruses cause most respiratory illness and most short-duration diarrhea. Antibiotics provide no benefit against viruses and have real side effects. The threshold for antibiotics is: bacterial pattern + localizing signs + systemic symptoms (fever above 100.4°F (38°C) with a wound, urinary burning with fever, productive cough with high fever and chest pain).

3. If someone has diarrhea, give ORS first — not Imodium. Loperamide (Imodium) slows gut motility and can prolong bacterial infection by keeping the pathogen in contact with the gut wall longer. ORS replaces the fluid and electrolytes lost. ORS is the first intervention; antidiarrheals are an adjunct at most.

4. Wake the adult in charge immediately if any of these are present: - Blood in stool, vomit, or urine - Fever above 103°F (39.4°C) in anyone over 3 months old - Confusion, disorientation, or unusual sleepiness in a sick person - Cannot keep any liquids down for 8 hours - Breathing fast (more than 20 breaths per minute at rest) or breathing hard - Stiff neck with high fever and headache - Red streak running from a wound toward the body

5. Isolate sick people to one room with their own cup and towel. The person caring for them should wash hands before and after every contact. If any respiratory illness is involved, keep the sick person's door closed and open a window in their room to move air outward. Provide a dedicated trash bag for their tissues and waste.

6. Cover coughs and sneezes with the inside of the elbow, not the hand. Hands immediately contaminate every surface they touch. The elbow is used less. Teach children to call this the "vampire cough" — it sticks.

7. Know the difference between a cold and pneumonia. Colds cause runny nose, sore throat, and mild cough — no high fever, the person can function. Pneumonia causes high fever (above 101°F / 38.3°C), productive cough with colored sputum, fatigue severe enough to prevent normal activity, and often a faster respiratory rate. A person who had a cold for 5–7 days and then got dramatically worse — worse fever, worse cough, worse fatigue — may have developed secondary bacterial pneumonia. That pattern warrants an antibiotic decision.

The Family Infection Briefing compiles these rules into a 6-page printable reference sheet at roughly an 8th-grade reading level — designed to hand to a teenager or non-medical household member.

Failure modes

These are the patterns most likely to cause harm in a prolonged off-grid or grid-down scenario. They are listed here separately from the "Teach your family" section because they require an adult with medical decision authority, not just household awareness.

Delayed recognition of sepsis. The qSOFA criteria — altered mental status, respiratory rate ≥22/min, systolic blood pressure ≤100 mm Hg — can be assessed without any equipment except a watch (to count breaths). Two of three criteria in a patient with a known infection source means probable sepsis and a transport emergency. This screen should be run every 6–12 hours on any patient with a wound infection showing systemic signs. See wound infection for the complete qSOFA protocol.

Treating dermatophyte (fungal) infection as bacterial cellulitis and vice versa. This is one of the most common misdiagnoses in field medicine precisely because both cause red skin. The cost of the error: antifungal cream applied to spreading cellulitis means the infection progresses for 48–72 hours without appropriate antibiotics. Conversely, oral antibiotics applied to athlete's foot with fissuring are ineffective, disrupt gut flora, and create C. diff risk.

Not completing antibiotic courses because supplies are rationed. In a prolonged scenario, rationing antibiotics across the household can mean everyone gets an inadequate course. Incomplete courses produce partially-resistant survivors. The correct approach: give one person the full course before starting another person on a second course, rather than splitting a single course between two people. Document antibiotic use carefully — this matters for every subsequent decision.

Assuming all GI illness is foodborne. Person-to-person transmission (norovirus, rotavirus, Shigella) requires isolation and hygiene interventions that are irrelevant if the outbreak source is a spoiled food batch. Differentiating matters: if multiple people became ill within 1–6 hours of eating the same food, the cause is likely a toxin or Salmonella; if illness spreads one person at a time over several days, person-to-person transmission is likely and isolation is the priority intervention.

Overconfidence in water treated by a single method. Boiling kills vegetative bacteria, viruses, and protozoa effectively at 212°F (100°C) for 1 minute (3 minutes above 6,500 feet / 2,000 m elevation). It does not remove chemical contaminants, heavy metals, or — critically — bacterial spores. Ceramic and hollow-fiber filters remove protozoa and bacteria physically but do not remove viruses without UV treatment or chemical disinfection. Using multiple methods in series (filter then boil, or filter then chemical treatment) provides broader coverage. See water boiling, water filtration, and chemical water treatment for the full multi-barrier approach.

The pages below connect directly to the content on this page. Use the syndrome pages when you have a specific presentation to manage; use this page when you need the underlying framework for why the syndrome pages make the recommendations they do.

When the Medical Foundation infectious disease expansion completes, this page will also link forward to: diarrhea and GI illness management, respiratory infection recognition and treatment, fungal skin infections, parasitic infections, and urinary tract infections.

Sources and next steps

Last reviewed: 2026-05-22

Source hierarchy:

  1. CDC Botulism Prevention — Home-Canned Foods (Tier 1, federal)
  2. USDA FSIS — Clostridium botulinum and Botulism (Tier 1, federal)
  3. CDC — C. diff Facts for Clinicians (Tier 1, federal)
  4. CDC — Norovirus Prevention (Tier 1, federal)
  5. CDC — Patient Care for Giardia Infection (Tier 1, federal)
  6. CDC — About Parasites (Tier 1, federal)
  7. WHO — Antimicrobial Resistance Fact Sheet (Tier 1, international standards)
  8. WHO — Bacterial Priority Pathogens List 2024 (Tier 1, international standards)
  9. NCBI Bookshelf — How Infection Works (Tier 1, NIH/academic)

Legal/regional caveats: Antibiotic prescribing authority varies by jurisdiction — in most US states, prescription antibiotics require a licensed prescriber. This page describes antibiotic selection for emergency preparedness education only. Permethrin products vary in concentration and formulation; follow label directions for the specific product obtained. Antifungal and antiparasitic medications have contraindications and interactions not fully covered here — check with a pharmacist or prescriber when possible.

Safety stakes: life-safety topic — verify against current local/professional guidance before acting.

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