Winter months bring more infections occurring indoors
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While visiting a neighbor’s home, a previously healthy 5-year-old boy was bitten on the right side of his face by an unleashed dog inside his neighbor’s home.
The dog’s immunization status was thought to be up to date, but the provocation was uncertain, so as a precaution, the dog was captured at its owner’s home and placed in quarantine by the veterinarian in coordination with animal control, and rabies prophylaxis was withheld. The child was seen in the local ER, where the wound was cleaned and one suture was placed, and he was sent home with a prescription for amoxicillin-clavulanate for prophylaxis. The parents stated that the child was up to date with all recommended immunizations at 15 months (including four doses of tetanus toxoid) but had none since then, stating that they choose not to immunize anymore. Two days later, the wound had become sore, with some purulent drainage and progressive swelling of the right side of his face and mild erythema (Figure 1). He was then admitted to the hospital for IV antibiotics and surgical drainage, with cultures of the wound and blood pending. Assuming the infection failed prophylaxis, it was thought to be likely due to MRSA, and vancomycin was started.
On hospital day 2 (4 days after the bite), he is found to have a fever (temperature of 104°F or 40°C), mild confusion, decreased urine output and a capillary refill of 4 to 5 seconds. His WBC count is 38,000, with 80% granulocytes; C-reactive protein is 87; and he has evidence of disseminated intravascular coagulation. His cultures are still negative at this time. Sepsis was clinically diagnosed, and ampicillin-sulbactam is added to his therapy. With this turn of events, a repeat history and complete exam is performed, revealing that the parents failed to mention that he has a history of abdominal trauma with the loss of his spleen 2 years ago, confirmed with an abdominal scar. They also admit that they do not give penicillin prophylaxis for the asplenia due to personal resistance to antibiotics in general and had not filled the initial prescription for amoxicillin-clavulanate prophylaxis.
What’s your diagnosis (the organism of greatest concern)?
A. Capnocytophaga canimorsus
B. MRSA
C. Pasteurella multocida
D. Eikenella corrodens
Answer and discussion
A dog bite in a patient with asplenia should immediately bring to mind Capnocytophaga canimorsus (choice A) as the organism of greatest concern. This is a slow-growing, gram-negative rod that is most commonly found in the mouths of dogs. In immunocompromised patients, especially patients with asplenia, this organism can progress to a severe opportunistic infection, including sepsis and meningitis, resulting in death in up to 30% if not promptly recognized and treated. Because it is a slow-growing, fastidious organism, the culture, if obtained, may take up to 7 days to become positive, and may therefore still be negative when symptoms appear. Amoxicillin-clavulanate is frequently given as dog bite, human bite or cat bite prophylaxis, and will normally prevent Capnocytophaga as well as the other, more common mouth organisms of dogs, cats and humans, but only if the patient takes it. At this time of great medical skepticism in our country, the number of parents who resist immunizations and antibiotics is growing, but they may be reluctant to admit it on the initial admission history. Therefore, when a patient takes an unexpected turn for the worse, a repeat history may reveal an answer.
The drug of choice for C. canimorsus infection would normally be IV penicillin G. If the patient developed sepsis while taking IV ampicillin-sulbactam, which is commonly used in hospitalized bite wound infections, a question of penicillin resistance should arise. In that case, a carbapenem, such as meropenem, would be a good choice, pending availability of culture and sensitivity data. Likewise, Staphylococcus aureus, including MRSA, would not likely emerge while being given IV vancomycin.
Pasteurella multocida, a common organism found in the mouths of cats, would not be expected to respond to vancomycin, making it much less likely or concerning. However, P. multocida does respond to amoxicillin, trimethoprim-sulfamethoxazole and fluoroquinolones. Being a dog bite does not rule out Pasteurella, but makes it much less likely. A classic human bite infection is typically caused by Eikenella corrodens, which is usually prevented with amoxicillin-clavulanate prophylaxis. Human bites can also be caused by group A strep or S. aureus.
The pattern of bite wounds can be indicative of the biting species. The pattern of a dog bite to the face usually produces puncture wounds at a time when the child is on the floor, playing with the dog, often near the food dish. The dog will “nip” the face and let go, as in the case presented. These bites are usually considered “provoked” by the child. In the event of a “dog attack,” usually outside the home, the result is typically that of a tearing wound of the arms, legs or trunk (Figure 2). Interestingly, these gapping wounds are less likely to become infected; however, as the patient presented has shown, a simple puncture wound is more prone to infection. A cat bite is virtually always a puncture wound, due to the nature of their teeth, making them more prone to infection (Figure 3), usually on the hand. Cat bite infections are classically caused by Pasteurella multocida, and as noted, should respond to amoxicillin-clavulanate as well.
Infected human “bites” are fairly uncommon. The most common pattern of a human “bite” that gets infected is the closed-fist injury in males (Figure 4), and usually caused by Eikenella corrodens, as noted above.
Columnist Comments
As our children (and grandchildren) spend more time indoors during these colder months, indoor accidents, animal bites by family pets and respiratory infections tend to increase. This would be a good time to point out something that I tripped upon when doing some dog bite research online. There is an abundance of videos on social media sites showing very young children, on the floor of family homes, in close proximity to pitbull dogs. These are intended to be cute, lovingly posed videos. However, they can quickly turn disastrous, with fatal outcomes, much like the “Russian roulette”-style risk that is played when children get their hands on a loaded gun. These horror stories will continue, but perhaps some increased awareness will help.For more information:
Brien is a member of the Healio Pediatrics and Infectious Disease News Editorial Boards, and an adjunct professor of pediatric infectious diseases at McLane Children's Hospital, Baylor Scott & White Health, in Temple, Texas. He can be reached at jhbrien@aol.com.