No, we haven’t forgotten: Haemophilus influenzae type b on the rise

I belong to the generation of doctors who didn’t grow up with Haemophilus influenzae type b. However, the U.S. literature is still fresh with descriptions of Hib clinical manifestations. This is a nasty bug. I just can’t imagine how overwhelmed we would be if Hib and methicillin-resistant Staphylococcus aureus hang out together in our communities.

At Texas Children’s Hospital, we see all flavors of MRSA. We see so much that once in a while we are fooled. However, you always have to raise an eyebrow when you elicit a history of incomplete immunizations. That is exactly what happened when my colleague and friend Luis Castagnini went to evaluate a previously healthy 4-year-old boy with a hot knee. The boy’s parents were concerned about side effects of vaccines, so they refused to vaccinate their two younger children (including our patient) and partially immunized two older school-aged children.

The child developed a fever to 103ºF. He was reluctant for us to get close to his left knee —that was swollen and very painful — had 23K WBC with C-reactive protein of 19 mg/dL and an erythrocyte sedimentation rate of 85 mm/h. The MRI revealed extensive inflammation of the soft-tissues and a focus of osteomyelitis in the proximal tibia. Gram-negative bacilli grew only in the chocolate-agar. The problem was subsequently identified as Hib. (Remember: Haemophilus influenzae needs fresh factors V and X in the agar plate, that are obtained by adding erythrocytes heated to 80ºC).

The patient was treated in-house with cefotaxime and completed a six-week course with parenteral ceftriaxone. Efforts were made to catch up with the vaccine schedule. Because of its infrequent presentation in our setting, Luis decided to report this case and concluded with the following remark:

“The importance of vaccinating all children and eliciting immunization history should be reinforced because, as this report illustrates, even in countries where Hib pharyngeal colonization has declined and invasive disease has been virtually eliminated through routine Hib vaccination, severe invasive disease due to Hib can occur in young children who are unimmunized.”

I have little to add to this conclusive remark.

Nevertheless, his report is more than opportunistic: five cases of invasive Hib were recently reported in Minnesota (MMWR 2009;58, Jan 23), where one of the patients died. The cases are viewed as a mix of parental reluctance to immunize their kids along with the ongoing Hib vaccine shortage.

The CDC and the American Academy of Pediatrics have issued recommendations in that regard. Invasive Hib numbers are on the rise (see the table in the MMWR report), and we all have to be prepared to enforce adherence to immunization schedules and to promptly detect new cases.

The 2006 Red Book recommendations about prophylaxis of contacts are excerpted here:

Indications and guidelines for rifampin chemoprophylaxis for contacts of index cases of invasive Haemophilus Hib disease

Chemoprophylaxis Recommended

For all household contacts¹ in the following circumstances:

• Household with at least one contact younger than 4 years of age who is unimmunized or incompletely immunized²
• Household with a child younger than 12 months of age who has not received the primary series
• Household with a contact who is an immunocompromised child, regardless of that child’s Hib immunization status
• For nursery school and child care center contacts when two or more cases of Hib invasive disease have occurred within 60 days

For index case, if younger than 2 years of age or member of a household with a susceptible contact and treated with a regimen other than cefotaxime or ceftriaxone, chemoprophylaxis usually is provided just before discharge from hospital

Chemoprophylaxis Not Recommended

• For occupants of households with no children younger than 4 years of age other than the index patient
• For occupants of households when all household contacts 12 to 48 months of age have completed their Hib immunization series and when household contacts younger than 12 months of age have completed their primary series of Hib immunizations
• For nursery school and child care contacts of one index case, especially those older than 2 years of age
• For pregnant women

¹ Defined as people residing with the index patient or nonresidents who spent four or more hours with the index case for at least five of the seven days preceding the day of hospital admission of the index case.

² Complete immunization is defined as having had at least one dose of conjugate vaccine at 15 months of age or older; two doses between 12 and 14 months of age; or a two or three dose.