Case 1: Man’s best friend?

A previously healthy six-week-old female infant presented with a one-day history of fever and irritability. She had a history of rhinorrhea and cough for 10 days before presentation. Further history revealed slightly decreased oral intake and loose, nonbloody stools. A normal number of wet diapers had been maintained.

Both parents had been sick with rhinorrhea and sore throats. The infant’s father had also experienced a recently active cold sore. The infant lived at home with her parents. There were no siblings or family pets. The week before presentation they had been visiting with friends who had a dog that licked the patient many times. The travel history was noncontributory.

The infant’s medical history was unremarkable. She was the product of an uncomplicated pregnancy, born at term by caesarean section due to failure to progress. Her birth weight was 3.75 kg. There were no infectious concerns during the perinatal period. Development and growth were normal to date. She had been exclusively breastfed, was not taking medications or supplements, and had no known drug allergies.

Initial assessment revealed a nontoxic but irritable infant weighing 4.7 kg (50th to 75th percentile). Length and head circumference were not measured. The vital signs were as follows: temperature 38.8°C (rectal), heart rate 203 beats/min (crying), blood pressure 88/37 mmHg, respiratory rate 40 breaths/min, O₂ saturation 97% on room air. Physical examination was unremarkable including the anterior fontanelle, which was soft and flat.

Initial laboratory testing revealed a hemoglobin level of 119 g/L, platelet count of 426×10⁹/L (normal range 150×10⁹/L to 400×10⁹/L), white blood cell count of 16.7×10⁹/L with 58% neutrophils, 17% bands and 22% lymphocytes, and a C-reactive protein level of 57.9 mg/L. Urinalysis was negative for nitrites and leukocytes. Urine and blood samples were sent for routine bacterial culture. Analysis of the cerebrospinal fluid (CSF) demonstrated a cloudy liquid with protein 0.33 g/L, glucose 2.93 mmol/L, red blood cell count 214×10⁶/L, and white blood cell count 1221×10⁶/L with 83.5% neutrophils, 6% bands and 1.0% lymphocytes. The Gram stain was negative. A CSF sample was sent for routine bacterial culture and molecular viral testing, and empirical treatment with intravenous cefotaxime, ampicillin and intravenous acyclovir was initiated. A diagnostic report was received after 24 h.

CASE 1 DIAGNOSIS: PASTEURELLA MENINGITIS

The CSF culture grew Pasteurella multocida. After the results of antibiotic sensitivity tests were returned, ampicillin was discontinued on day 6 of admission and cefotaxime was continued for a 14-day course. A repeat lumbar puncture was performed on day 4 of admission, and the culture was negative. The Infectious Disease service was consulted to guide therapy and the patient was seen as an outpatient by the immunology department to rule out an underlying immunodeficiency. The infant’s age, in combination with extensive contact with a dog, was considered to be an explanation for her illness.

P multocida is a rare but serious cause of neonatal meningitis. P multocida is a pleomorphic Gram-negative coccobacillus found in the mouths of many species of animals, particularly cats (70% to 90%) and dogs (50% to 66%). In humans, it is the most common cause of infection after a dog bite, but is also known to cause bacteremia, pneumonia, septic arthritis, conjunctivitis and meningitis (1).

To date, 38 cases of infant P multocida meningitis have been reported in the English-language literature. The age was known for 36 of the cases, and 30 infants were ≤3 months of age. Of all 38 cases, 31 patients (82%) had been exposed to animals and, of those exposures, 27 (87%) were nontraumatic and only four (13%) were traumatic (eg, bites or scratches). The most likely route of transmission when the contact is nontraumatic is from exposure to the animal’s oropharyngeal secretions. This exposure can come from direct licking or sniffing, or from being handled by someone who did not wash their hands after contact with a pet. The neonate may then develop pharyngeal colonization with P multocida, which can be followed by invasion and hematogenous spread to the meninges (2).

Complications from P multocida meningitis are similar to other causes of meningitis and include seizures, hemiparesis, brain abscesses, hydrocephalus and, rarely, death (two cases reported). Therefore, although P multocida is a relatively rare cause of neonatal meningitis, the consequences are potentially devastating (2). With this in mind, it is recommended that very young infants should not come in contact with the saliva of cats or dogs, and that anyone in contact with pets should wash their hands before handling an infant. Pacifiers that may have come in contact with an animal should be thoroughly washed before use. These simple measures will help prevent future cases of neonatal P multocida meningitis (1,2).

The present case also raises the issue of indications for repeat lumbar puncture. For our patient, a lumbar puncture was repeated on day 4 of treatment. Resultant CSF analysis demonstrated a reduced white blood cell count of 18 × 10⁶/L, with a shift to a lymphocyte predominance of 60%. Notably, the CSF bacterial culture from this repeat lumbar puncture was negative. There is very little evidence to guide clinicians on whether to repeat a lumbar puncture in cases of bacterial meningitis. The Canadian Paediatric Society recommends repeating a lumbar puncture in patients who fail to improve clinically within 24 h to 36 h on antibiotics, in immunocompromised patients in whom the success of antibiotic therapy cannot be assured, in patients with meningitis caused by a gram-negative enteric bacillus, and in patients with meningitis caused by penicillin- or cephalosporin-resistant pneumococcus. If the repeat lumbar puncture reveals evidence of untreated or partially treated infection, reassessment of antimicrobial therapy is required.

CLINICAL PEARLS

• Anticipatory guidance to new parents should include keeping very young infants away from cats and dogs. In addition, anyone in contact with animals should wash their hands before handling the infant and pacifiers should be cleaned before use. It should be emphasized that even nontraumatic contact with pets can lead to infection.

• There is little evidence to guide physicians on when to repeat a lumbar puncture. The Canadian Paediatric Society recommends repeating a lumbar puncture in patients who fail to improve within 24 h to 36 h on antibiotics, in immunocompromised patients, in patients with meningitis caused by a Gram-negative enteric bacillus, and in patients with meningitis caused by penicillin- or cephalosporin-resistant pneumococcus.

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