Doctors prescribe antibiotics when they believe a bacterial infection is causing your symptoms, or when the risk of a bacterial complication is high enough to justify treatment. That sounds simple, but the decision is surprisingly nuanced. Most infections people visit a doctor for, especially coughs, colds, and sore throats, are caused by viruses, and antibiotics do nothing against viruses. The real question your doctor is weighing is whether bacteria are the likely culprit, and several specific rules and scoring systems help them decide.
Why the Bacterial vs. Viral Distinction Matters
Bacterial and viral infections often look almost identical in the exam room. You can have a fever, fatigue, and thick mucus with either one. To get past that similarity, doctors rely on symptom patterns, timing, and sometimes blood tests. One key marker is C-reactive protein (CRP), a substance your liver releases during inflammation. In bacterial infections, CRP levels average around 133 mg/L on admission, compared to roughly 23 mg/L for viral infections. When CRP climbs above 275 mg/L, the infection is almost always bacterial.
But most visits don’t involve blood work. For common outpatient illnesses like sore throats, sinus infections, ear infections, and urinary tract infections, doctors use symptom-based checklists and timelines instead.
Sore Throats and the Scoring System
Most sore throats are viral. To figure out which ones are bacterial (usually strep), doctors use a checklist called the Centor score. You get one point for each of four things: swollen lymph nodes in your neck, fever, white or yellow patches on your tonsils, and the absence of a cough. A cough actually makes strep less likely, because it suggests a viral upper respiratory infection instead.
A score of 0 or 1 generally means no antibiotics. A score of 2 or 3 puts you in a gray zone where your doctor may order a rapid strep test or give you a delayed prescription to fill only if you don’t improve. A score of 4 or 5 (on a related scale called FeverPAIN, which also factors in symptom duration under three days and severity of tonsillar inflammation) is associated with a 60 to 65 percent chance of streptococcal infection, and that’s typically enough to prescribe antibiotics right away.
Sinus Infections Have a Time Rule
Sinus infections are one of the most over-treated conditions. Fewer than 5 percent of sinus infections are actually bacterial. The rest are viral and will clear on their own. Doctors use three specific patterns to identify the bacterial cases:
- Persistent symptoms: Congestion, facial pressure, and nasal discharge that haven’t improved at all after 10 days suggest bacteria have taken hold.
- Severe onset: A fever above 102°F (39°C) combined with thick, discolored nasal discharge or facial pain lasting more than 3 days from the start of illness points toward a bacterial cause.
- Double sickening: You start to feel better from what seems like a normal cold, then around day 5 or 6, symptoms suddenly worsen with a new fever, worse headache, or increased nasal discharge. This rebound pattern is a classic sign that a secondary bacterial infection has developed.
If none of these three patterns apply, your doctor will likely recommend decongestants, saline rinses, and time rather than antibiotics.
Ear Infections Depend on Age and Severity
For children’s ear infections, the decision depends heavily on how old the child is and whether one or both ears are affected. Infants under 6 months get antibiotics immediately, because there isn’t enough safety data to support a wait-and-see approach in babies that young. Children between 6 and 24 months get immediate antibiotics if both ears are infected, regardless of how severe it looks. But if a child in that age range has a mild infection in just one ear, doctors can safely watch and wait.
For children over 2 and teenagers, watchful waiting is the default for uncomplicated ear infections in one or both ears. The exception is when symptoms are severe: fluid draining from the ear, high fever, or a visibly sick child. In those cases, antibiotics start right away. When doctors do use a wait-and-see approach, the typical observation window is about three days before filling a prescription.
Urinary Tract Infections Are More Straightforward
UTIs are one of the clearer-cut cases for antibiotics. In otherwise healthy women of childbearing age, the combination of new painful urination and frequent urination, without vaginal discharge, is enough to diagnose a UTI and start antibiotics. A urine dipstick test showing nitrites and white blood cells confirms the diagnosis, but the symptom pattern alone is considered reliable.
The straightforwardness here comes from the fact that UTIs are almost always bacterial. Unlike sore throats or coughs, there isn’t a viral version that mimics the same symptoms. That’s why doctors are comfortable prescribing quickly for UTIs while taking a more cautious approach with respiratory symptoms.
Pneumonia Uses a Severity Score
When a doctor suspects pneumonia, antibiotics are almost always part of the treatment. The bigger question is where you’ll be treated: at home or in the hospital. A scoring tool called CURB-65 helps answer that. It assigns one point each for confusion, elevated blood urea levels, a breathing rate of 30 or more breaths per minute, low blood pressure, and being 65 or older. A score of 0 to 2 usually means you can recover at home with oral antibiotics. A score of 3 to 5 signals higher mortality risk and typically means hospital admission with stronger, intravenous treatment.
The Delayed Prescription Strategy
For borderline cases, many doctors use a strategy called a delayed prescription. They write an antibiotic prescription but ask you not to fill it immediately. Instead, you wait a set number of days, and if symptoms haven’t improved or have worsened, you go ahead and pick up the medication. The delay period varies by condition: about three days for ear infections, and up to 10 days for a persistent cough.
This approach works because most infections that seem borderline turn out to be viral, and symptoms resolve on their own. Studies show that delayed prescriptions significantly reduce unnecessary antibiotic use, because a large portion of patients never end up filling them.
Why Doctors Are Cautious About Prescribing
The push to limit unnecessary antibiotics isn’t just about antibiotic resistance at a population level. Antibiotics carry real, personal side effects. Diarrhea is one of the most common: it affects 10 to 15 percent of people taking certain types and up to 20 percent with others. Skin rashes occur in 5 to 10 percent of people taking common antibiotics like amoxicillin. Some antibiotics also carry a significant risk of C. difficile infection, a potentially dangerous gut infection caused by wiping out your normal intestinal bacteria.
These risks are worth taking when you genuinely have a bacterial infection. A course of antibiotics for confirmed strep throat prevents complications like rheumatic fever. Treating a UTI prevents it from spreading to the kidneys. Pneumonia antibiotics can be lifesaving. But when the infection is viral, you take on all of these side effects for zero benefit. That trade-off is why your doctor sometimes says no, or asks you to wait a few days and see how things develop, even when you feel miserable and want a prescription now.