Dog Bite Infections: Bacteria, Symptoms, Treatment, and Your Legal Rights in California

Dog bite wounds carry bacteria into tissue where they can multiply fast. Between 3% and 18% of dog bites become infected — and without antibiotic prophylaxis, a meta-analysis of eight randomized trials put the infection rate at 16%. Some infections stay at the surface. Others reach the bloodstream within days and require hospitalization, surgery, or IV antibiotics for weeks.

Most people who get bitten focus on the wound itself — whether it needs stitches, whether it will scar. The infection risk gets underestimated, often because the bite didn’t look that bad at first. At our firm, we’ve handled Sacramento dog bite cases where the client came to us after being bitten with a wound that seemed manageable and eventually turned into a hospitalization, a course of IV antibiotics, and months of follow-up care that no early settlement offer had accounted for. 

Knowing which bacteria cause the most serious infections, what symptoms to watch for, and how documented medical treatment connects to your legal claim — that’s the purpose of this page.

How Often Dog Bites Become Infected

Approximately 4.5 million Americans are bitten by dogs each year. Roughly 300,000 of those bites result in emergency department visits, and around 10,000 lead to hospitalizations, according to research published in the New England Journal of Medicine. Dog bites account for 1% of all injury-related ER visits in the United States and more than $50 million in annual inpatient costs.

The 3% to 18% infection rate reflects real variability. Wound depth, location, time to treatment, and immune status all move that number. Hand wounds carry the highest risk — in one study cited by the American Academy of Family Physicians, antibiotic prophylaxis reduced the infection rate in hand wounds from 28% to 2%. Bites to the face, feet, and joints carry elevated risk for different reasons: proximity to tendons, joints, and bone.

Hundreds of Bacteria Live in a Dog’s Mouth

A dog’s mouth is home to hundreds of bacterial species. When a dog bites, those organisms are driven into subcutaneous tissue, where they encounter a warm, protein-rich environment that supports growth. Most infected dog bite wounds involve more than one pathogen simultaneously — 56% of infections are polymicrobial, according to the landmark bacteriologic study published in the New England Journal of Medicine.

The five organisms that cause the most clinically significant infections are Pasteurella, Capnocytophaga canimorsus, Staphylococcus aureus (including MRSA), Streptococcus, and anaerobic bacteria.

Pasteurella: Fast, Common, and Treatable If Caught Early

Pasteurella is the most frequently isolated pathogen in infected dog bites. The CDC’s Emerging Infectious Diseases journal reports it is present in approximately 50% of infected dog bite wounds. The species most commonly found in dog bites specifically is Pasteurella canis, though Pasteurella multocida — which predominates in cat bites — also appears.

Pasteurella acts fast. Cellulitis typically develops within 24 hours of the bite. The wound becomes red, warm, swollen, and painful — and pain that was easing starts getting worse. Untreated, Pasteurella extends into deeper structures, causing septic arthritis (bacterial infection of a joint), osteomyelitis (bone infection), bacteremia (bacteria circulating in the bloodstream), meningitis, and endocarditis. Puncture wounds to the hand are especially prone to septic arthritis because the bacteria can be inoculated directly into a tendon sheath or joint space with very little surface-level evidence of how deep the wound actually went.

Pasteurella multocida is almost universally sensitive to penicillin. Amoxicillin/clavulanate covers it reliably and is the first-line treatment recommended by the Infectious Diseases Society of America (IDSA).

Capnocytophaga canimorsus: Slow Onset, Very Lethal

Capnocytophaga canimorsus is the organism most likely to kill an otherwise healthy adult following a dog bite, and it deserves more attention than it typically gets.

Culture-based studies have detected C. canimorsus in roughly 20–57% of dogs depending on sampling method and population; PCR-based detection, which is more sensitive, has found it in up to 74% of dogs in some studies (Suzuki et al., Veterinary Microbiology, 2010). Despite how common it is in dog saliva, human infections are rare — approximately 0.5 to 0.7 cases per million people per year. That low incidence is partly explained by recent capsular serovar research from the Cornelis laboratory: of the nine or more known serovars of C. canimorsus, three serovars (A, B, and C) cause roughly 90% of documented human infections, but those three serovars account for only about 7.6% of isolates found in dog mouths (Emerging Infectious Diseases, 2018; Emerging Microbes and Infections, 2018). Most dogs are carrying strains that don’t commonly cause human disease. But you cannot know which ones without genomic testing that doesn’t exist in clinical practice.

The organism was first identified in 1976 by Bobo and Newton, who isolated it from a patient presenting simultaneously with meningitis and sepsis after two consecutive dog bites. For years, the CDC labeled it DF-2 — dysgonic fermenter — because it grows so slowly in laboratory cultures that standard identification systems routinely missed it.

The clinical picture is what makes C. canimorsus dangerous. Symptoms typically begin 3 to 5 days after the bite, sometimes up to two weeks later. They start as fever, diarrhea, vomiting, and headache — easy to dismiss as a stomach virus — while the wound itself may look unremarkable. Once systemic, the infection can progress within hours to septic shock and a condition called disseminated intravascular coagulation (DIC). DIC is a cascade in which the blood simultaneously clots abnormally throughout the body and loses the ability to clot where it needs to: the result is simultaneous thrombosis and bleeding, which can cause gangrene, limb amputation, organ failure, and death. The CDC lists documented complications including myocardial infarction, renal failure, and amputation.

A review of 56 C. canimorsus isolates submitted over 32 years to California’s Microbial Diseases Laboratory — the largest such series in the published literature at the time — found a case fatality ratio of 33% (Janda et al., Emerging Infectious Diseases, 2006). That figure is consistent with two other clinical series (30–31%). It is important to understand what these numbers represent: they come from confirmed, severe cases submitted to reference laboratories for identification, not from all people who were bitten and developed any infection. The true population-level fatality rate for C. canimorsus infection is substantially lower, in part because milder cases are never identified to species. Even so, the 30–33% mortality rate in confirmed, hospitalized cases is among the highest of any common dog bite pathogen.

Why asplenic patients face the greatest danger. The spleen is the body’s primary filter for encapsulated bacteria — organisms like C. canimorsus that use a polysaccharide capsule to evade the immune system. The spleen produces IgM antibodies and tuftsin, a peptide that signals macrophages to begin phagocytosis (engulfing and destroying bacteria). Without a functional spleen, encapsulated bacteria are not tagged for destruction effectively, and C. canimorsus exploits this gap. Research from the Cornelis lab has identified two distinct virulence factors that help explain how C. canimorsus overwhelms the immune system: a sialidase enzyme, present in all tested dog strains, that removes sugar molecules from host cell surfaces; and a separate capacity, found in roughly 60% of dog strains tested, to directly block macrophages from killing bacteria they have already engulfed. These are two independent mechanisms, and their combination makes the organism particularly dangerous in patients whose immune systems are already compromised. People without a spleen — due to splenectomy, sickle cell disease, or congenital asplenia — should tell any treating physician immediately after a dog bite. Prophylactic antibiotics before symptoms appear are warranted.

Other high-risk conditions include diabetes mellitus, liver cirrhosis, Hodgkin lymphoma, and long-term use of corticosteroids or other immunosuppressants. Alcohol use disorder appears as a predisposing factor in 18–24% of C. canimorsus cases in some European series.

Staphylococcus, MRSA, and Streptococcus

Staphylococcus aureus appears in 30–50% of infected dog and cat bite wounds, according to the Johns Hopkins ABX Guide. MRSA — the methicillin-resistant strain — does not respond to standard beta-lactam antibiotics like amoxicillin. Research in the International Journal of Oral and Maxillofacial Surgery has documented that MRSA in pets is frequently acquired from their human household members, creating a bidirectional transmission loop: a household member carries MRSA, the dog’s mouth picks it up, and a bite reintroduces it through the skin. When MRSA is confirmed or suspected from culture results, the IDSA recommends trimethoprim-sulfamethoxazole, doxycycline, or clindamycin rather than beta-lactams.

Streptococcus species cause rapid-onset spreading redness and swelling, often within hours. In children, streptococcal infections from dog bites can advance from localized cellulitis to bacteremia quickly.

Anaerobic Bacteria and Deep Puncture Wounds

Anaerobic bacteria require low-oxygen environments to grow. Puncture wounds — common in dog bites and particularly dangerous for this reason — create exactly those conditions. When a dog’s canine tooth drives through skin and subcutaneous tissue, it crushes the surrounding cells, destroying the small blood vessels (capillaries) that would otherwise deliver oxygen to the tissue. That devitalized, poorly perfused space at the bottom of a puncture tract is oxygen-depleted, which is precisely where anaerobes thrive.

The most clinically significant anaerobes in dog bite infections include Bacteroides, Fusobacterium, Porphyromonas, and Prevotella. The landmark 1999 New England Journal of Medicine bacteriologic study found fusobacterium, bacteroides, porphyromonas, and prevotella as the predominant anaerobic isolates, and identified several species that had not previously been documented in human dog bite infections. Anaerobes rarely act alone; they amplify the damage caused by the aerobic organisms present in the same wound.

Who Faces the Highest Infection Risk

The IDSA recommends routine prophylactic antibiotics for bite wounds with any of the following characteristics, even before symptoms appear.

Wound features that predict infection:

• Puncture wounds, particularly to the hands
• Bites overlying joints, tendons, or bone
• Crush injuries with devitalized tissue
• Wounds presenting more than 12 hours after the bite
• Any wound where primary irrigation was delayed

Patient characteristics that predict severe infection:

• Absence of a spleen (any cause)
• Diabetes mellitus
• Liver cirrhosis or chronic liver disease
• Active cancer or recent chemotherapy
• Immunosuppressive medications, including corticosteroids and biologics
• Alcohol use disorder
• Age over 50: 70% of patients in the California MDL C. canimorsus series were over 50 years old

Children are the demographic most frequently bitten, but they are not the group most likely to develop life-threatening systemic infection. Middle-aged and older adults with underlying health conditions carry the heaviest burden of severe outcomes.

How Infections Develop After a Bite

At the time of the bite: Bacteria from saliva and the skin surface enter the wound. No visible infection yet.

12 to 24 hours: Pasteurella infections declare themselves. Pain that was improving reverses. Redness spreads outward from the wound margin. Warmth and swelling increase.

24 to 48 hours: Cellulitis becomes visible. The redness expands. Lymphangitic streaking — thin red lines tracking up the limb toward a lymph node — signals bacterial spread through the lymphatic system and requires emergency evaluation.

3 to 5 days (up to 14 days): Capnocytophaga symptoms emerge. Fever, diarrhea, vomiting, headache. The wound may look unremarkable while the patient becomes systemically ill. Deterioration can follow rapidly.

At any point if untreated: Sepsis — the body’s uncontrolled inflammatory response to infection — can develop from any of these organisms. Fever above 100.4°F (38°C), heart rate above 100 beats per minute, confusion, and low blood pressure are sepsis warning signs. Every hour of delayed treatment worsens outcomes.

Recognizing an Infected Wound

At the wound:

• Redness spreading past the initial bruised area
• Swelling that worsens after the first 48 hours
• Warmth that radiates beyond the wound edges
• Pus or discharge — yellow, green, or foul-smelling
• Pain that increases rather than gradually easing
• Red streaks extending from the wound toward the lymph nodes

Whole-body signs:

• Fever above 101°F
• Chills or night sweats
• Swollen lymph nodes in the armpit, groin, or neck
• Nausea, vomiting, or diarrhea beginning several days after the bite
• Headache or confusion
• Fatigue disproportionate to the injury
• Rapid heartbeat

The Capnocytophaga presentation — diarrhea, vomiting, headache, and fever appearing 3 to 5 days after a bite — is frequently attributed to a stomach virus. If those symptoms follow a recent dog bite, report the bite history to the treating physician immediately. C. canimorsus requires specific blood cultures; many clinical labs still have difficulty identifying this organism accurately and may need to send the specimen to a reference lab.

Emergency Room vs. Urgent Care

Go to the emergency room:

• Fever combined with confusion or altered mental status
• Red streaks spreading from the wound
• Bite to the hand or face with lost sensation, range of motion, or grip
• Any puncture wound in an immunocompromised or asplenic patient
• Suspected joint or bone involvement
• Signs of sepsis: fever, rapid heartbeat, dizziness when standing, difficulty breathing

Urgent care is appropriate for:

• Superficial abrasions requiring cleaning and tetanus update
• Follow-up for established, responding infections

If there is any uncertainty about severity, go to the emergency room. Dog bite infections can move from localized to systemic within 24 hours.

How Doctors Treat Dog Bite Infections

Irrigation is the most important single intervention. Physicians irrigate bite wounds with normal saline using a syringe of at least 20mL — the pressure is what matters, not the volume alone. This physically reduces the bacterial load before antibiotics are started.

Wound exploration assesses for tendon, joint, or bone involvement and looks for tooth fragments. A bite that overlies a joint and causes pain during passive range of motion raises suspicion for septic arthritis, which requires surgical washout, not antibiotics alone.

Antibiotics: Amoxicillin/clavulanate (Augmentin) is first-line per the IDSA’s skin and soft tissue infection guidelines. It covers Pasteurella, Streptococcus, susceptible Staphylococcus, and oral anaerobes. For high-risk bites, 3 to 7 days of prophylaxis is standard. Established infections typically require 10 to 14 days. For penicillin allergy, the IDSA recommends clindamycin combined with either doxycycline or trimethoprim/sulfamethoxazole. MRSA requires trimethoprim/sulfamethoxazole, doxycycline, or clindamycin. Systemic infections involving joints or bone require IV antibiotics and hospital admission.

Wound closure: The IDSA recommends against primary closure for most dog bites — closing the wound traps bacteria in the tissue. Facial wounds are the exception, where blood supply is rich enough and cosmetic stakes high enough to justify cautious closure with concurrent antibiotics. Most other wounds are left open or approximated loosely, with delayed primary closure considered after 3 to 5 infection-free days.

Tetanus: A booster is recommended if more than 5 years have passed since the last shot, or 10 years for a clean, minor wound. When in doubt, get the booster.

Rabies: More than 90% of U.S. rabies cases occur in wildlife — bats, raccoons, skunks, and foxes — not domestic dogs. If the biting dog is known, healthy, and can be observed for 10 days, rabies post-exposure prophylaxis (PEP) can be deferred. If the dog is unavailable, stray, or behaving abnormally, PEP should begin immediately. Once rabies symptoms appear, survival is extremely rare. PEP started before symptoms is nearly 100% effective.

How Infection Affects Your California Dog Bite Claim

Under California Civil Code § 3342, a dog’s owner is strictly liable for injuries caused by a bite on public property or lawfully-visited private property, regardless of whether the dog had any prior history of aggression. The owner cannot avoid liability by claiming the dog had never shown aggression before. Learn more about how California’s strict liability statute applies to your case.

A bite that becomes infected changes what you are owed.

Medical costs multiply. A laceration might involve one ER visit and a prescription. An infected wound can produce multiple follow-up appointments, IV antibiotics, surgical drainage of an abscess, hospitalization for sepsis, plastic surgery for deep scarring, or months of physical therapy for a hand with nerve or tendon damage. Every cost is in your medical records, which form the evidentiary foundation of your claim. Read about the four main categories of dog bite injuries and their legal significance.

Lost income is documentable. An infection requiring a week of hospitalization and four weeks of restricted hand use is a wage loss claim that pay stubs and employment records can support precisely.

Scarring is compensable separately. California law treats permanent disfigurement as a distinct category of harm from medical costs. Bites to the face and hands — the wounds most prone to Pasteurella and polymicrobial infection — are also the wounds where scarring carries the most weight in a damages calculation.

Settling early is a specific risk in infection cases. A dog bite infection may require months of treatment — surgery, scarring revision, physical therapy — that is not foreseeable in the first week. Accepting an early settlement releases the dog owner and their insurer from any further liability, including treatment not yet started. Contact a Sacramento dog bite lawyer before responding to any settlement offer or agreeing to give a recorded statement.

The statute of limitations for a dog bite personal injury claim in California is two years from the date of the bite (California Code of Civil Procedure § 335.1). If the victim is a minor, the limitations period is tolled until age 18. Our Sacramento personal injury attorneys can review the specific deadline in your situation at no charge.

Frequently Asked Questions

The wound looked minor at first. Can it still become a serious infection? Yes — and puncture wounds are specifically deceptive. When a canine tooth enters and withdraws from skin, the surface closes quickly, trapping bacteria in deeper tissue where oxygen is limited and immune surveillance is reduced. Capnocytophaga infections frequently begin with a wound that looks unremarkable. The fever, vomiting, and confusion that signal systemic illness arrive 3 to 5 days later, often in patients who never had dramatic local wound changes.

I have diabetes. Does that change my risk? Substantially. Diabetes impairs both the vascular supply to extremities and the immune response to bacterial infection. The IDSA and hospital-based guidelines recommend prophylactic antibiotics for diabetic patients after any dog bite, not just high-risk wounds. Diabetic patients with established dog bite infections are more likely to require hospitalization and IV antibiotics than immunocompetent patients with comparable wounds.

What are the red streaks I’m seeing near my wound? Those streaks are lymphangitis — inflammation of the lymphatic vessels as bacteria spread through them toward a lymph node. It typically appears as thin red lines tracking up an arm or leg from the bite site. Go to the emergency room. Lymphangitis can advance to sepsis, and that progression does not pause while you monitor the situation at home.

My own dog bit me. Do I still need to see a doctor? Yes. Your dog’s mouth carries the same bacterial species as any other dog. Pasteurella, Staphylococcus, and Capnocytophaga are normal residents of domestic dog saliva regardless of vaccination status, diet, or how well the animal is cared for. Bacteria don’t distinguish between familiar people and strangers.

How does documented infection affect what I can recover in a claim? Every medical record connected to your infection — the ER visit, culture and sensitivity results, antibiotic prescriptions, follow-up records, surgical notes, wound photographs — is evidence an attorney uses to document and support your damages for medical expenses, lost wages, and pain and suffering. Gaps in documentation give insurers grounds to argue that treatment was unnecessary or caused by something unrelated to the bite. See a physician promptly after any bite. Follow up as directed. Keep records of everything.

Can a dog bite infection be fatal? In rare cases, yes. The NEJM study estimated approximately 20 deaths annually from animal bites in the United States. Confirmed Capnocytophaga canimorsus infections in clinical case series have carried mortality rates of 30–33%, though these figures represent hospitalized, confirmed cases — not the full spectrum of people bitten. Sepsis from any of the bacteria discussed on this page carries significant mortality that rises for every hour treatment is delayed. If a family member dies from complications of a dog attack, California law allows surviving relatives to pursue a wrongful death claim.

Speak with a Sacramento Dog Bite Attorney

If a dog bite left you with an infection, documented medical treatment, or lasting complications, you have legal rights under California Civil Code § 3342 regardless of the dog’s prior history.

J&Y Law represents dog bite victims throughout Sacramento County, including Elk Grove, Roseville, Folsom, and surrounding communities. The consultation is free, and we handle cases on a contingency basis — no fee unless we recover money for you.

Call or text (877) 735-7035 — 24 hours a day, 7 days a week.