VACCINE AGAINST PNEUMOCOCCAL DISEASE IS EFFECTIVE AND UNDERUSED

Despite the availability of a vaccine against Streptococcus pneumoniae, more than 60,000 cases of invasive pneumococcal disease still occur in this country every year. Some groups—including young children, the elderly, and black patients—remain disproportionately affected by this disorder. More than half of all cases, however, could be avoided if current vaccination guidelines were followed more closely.

Robinson et al used data from the nine-state Active Bacterial Core Surveillance/ Emerging Infections Program Network to identify cases of invasive pneumococcal disease. They found that in 1998 the overall incidence of invasive disease in this sample was 23.2 cases per 100,000 people; this translates to an estimated 62,840 cases in the United States each year.

Incidence per 100,000 people was highest at the extremes of age: 166.9 in children younger than 2 years and 59.7 among adults 65 years or older. As a result, 53% of all cases were found to occur in these two groups. Incidence also depended on race: 49.7 in blacks compared with 19.7 in whites.

Robinson and colleagues also calculated case-fatality rates based on their nine-state sample. These rates ranged from 1.4% among those younger than 2 years to 20.6% among those 80 years or older. Death was more likely to occur in patients with pneumococcal meningitis than in those with pneumonia or bacteremia.

Among patients ages 18 to 64 years, 59% had at least one condition that has been identified by the Advisory Committee on Immunization Practices (ACIP) as an indication for pneumococcal vaccination. Because the case-fatality rate for these patients was more than twice what it was for age-matched patients without an ACIP indication, the authors urge that a greater effort be made to vaccinate all appropriate patients. This should significantly reduce the incidence of the disease.

Robinson KA, Baughman W, Rothrock G, et al. Epidemiology of invasive Streptococcus pneumoniae infections in the United States, 1995-1998: opportunities for prevention in the conjugate vaccine era. JAMA. 2001;285:1729-1735.

OFFICE OXIMETRY PREDICTS OXYGEN DESATURATION

Oxygen desaturation caused by physical exertion can be predicted in patients with chronic obstructive pulmonary disease (COPD) using baseline oxygen saturation obtained through standard pulse oximetry (SpO2). The authors of a retrospective study determined that this measurement offers especially clear information about desaturation when combined with assessment of diffusion capacity of lung for carbon monoxide (DLCO).

Knower et al examined 81 patients who were tested for exercise-induced desaturation and who also had a forced expiratory volume in one second/forced vital capacity ratio of 70% or less. The study group was divided according to their baseline SpO2 measurements: 96% or more and 95% or less. DLCO levels in all patients had been previously documented.

Of the 37 patients with a resting SpO2 of 95% or less, 19 (51%) experienced clinically significant desaturation (defined as 88% or less) during a walking exercise. Only seven (16%) of the 44 patients with a resting SpO2 of 96% or greater desaturated to that level. Of particular interest was that no patients with DLCO levels above 36% and resting SpO2 levels of 96% or more experienced clinically significant desaturation.

This combination—a DLCO level of 36% or more and baseline SpO2 of at least 96%—demonstrated 100% sensitivity as a screening tool for exercise desaturation. Knower et al concluded that when combined with information about a patient’s DLCO level, basic office oximetry can help physicians determine which patients need further exercise testing to determine how their COPD will be treated.

Knower MT, Dunagan DP, Adair NE, Chin R Jr. Baseline oxygen saturation predicts exercise desaturation below prescription threshold in patients with chronic obstructive pulmonary disease. Arch Intern Med. 2001;161:732-736.

THERMAL STRESS AS A CAUSE OF SIDS

Both rebreathing suffocation and thermal stress have been implicated in the development of sudden infant death syndrome (SIDS); however, the two have in common many risk factors, including prone sleeping and bed sharing. Thus, it has not been clear whether thermal stress independently increases the risk of SIDS. Guntheroth and Spiers now report that some deaths attribted to thermal stress cannot be explained by rebreathing.

These researchers reviewed the literature to evaluate the role of thermal stress and its relationship to rebreathing suffocation as a cause of SIDS. (Rebreathing refers to the effect that occurs when the infant inhales carbon dioxide that has accumulated in the bedding [with a concomitant loss of oxygen]; this eventually results in death.) In addition to prone sleeping and bed sharing, risk factors for both thermal stress and rebreathing include covering the infant’s head, swaddling, use of a soft mattress and pillows, and sleeping on sheepskin. However, other known risk factors for SIDS—excessive sweating, infection with fever, high room temperature, excessive bedclothes, and passive exposure to cigarette smoke—support the idea of thermal stress but not of rebreathing as a cause of SIDS.

The seasonal distribution of SIDS deaths also argues for thermal stress as a cause of SIDS. Fewer deaths occur in summer, when parents are most likely to dress their infants in light clothing.

The authors note that regardless of etiology, preventive programs should stress avoiding prone sleeping, soft bedding, and covering the infant’s head. However, they argue that a public education campaign that also emphasizes the dangers of thermal stress might further reduce the risk of SIDS.

Guntheroth WG, Spiers PS. Thermal stress in sudden infant death: is there an ambiguity with the rebreathing hypothesis? Pediatrics. 2001;107:693-698.

PULMONARY FUNCTION INCREASES AFTER SCOLIOSIS TREATMENT

Most patients with adolescent idiopathic scoliosis who are treated with posterior spinal surgery or bracing experience improved pulmonary function for up to 25 years after treatment, say the authors of a long-term follow-up study.

Pehrsson et al examined lung volumes and respiratory symptoms in 251 patients who had been treated for adolescent idiopathic scoliosis at least 20 years earlier: 141 treated surgically with posterior fusion and 110 with a brace. One hundred age- and gender-matched subjects without scoliosis served as controls.

All 251 scoliosis patients had undergone lung volume measurements before surgery or bracing. Repeat measurements were obtained a mean of 1.4 years after treatment in the surgical patients and a mean of 25 years after treatment in both groups.

Among the surgical patients, vital capacity (VC) as a percentage of predicted was 67% before treatment, 73% at the 1.4-year follow-up, and 84% at the most recent follow-up; forced expiratory volume in one second (FEV1) as a percentage of predicted was 71%, 78%, and 84%, respectively. Among the patients given braces, predicted VC rose from 77% before treatment to 89% at follow-up; predicted FEV1 increased from 84% to 91%. None of these measurements of lung volume were significantly different from those of controls.

The incidence of dyspnea was similarly low (3% or less) in all three groups. Wheezing was slightly more common in the scoliosis patients (33% in the surgical patients; 30% in those given braces) than in the controls (23%), but the difference did not reach significance.

The mean Cobb angles in the two treatment groups were 62° and 33°, respectively, before treatment, and 37° and 38°, respectively, at the 25-year follow-up. Neither pretreatment nor posttreatment Cobb angles correlated with the patients’ adult lung volumes.

Pehrsson K, Danielsson A, Nachemson A. Pulmonary function in adolescent idiopathic scoliosis: a 25 year follow up after surgery or start of brace treatment. Thorax. 2001;56:388-393.

EXOGENOUS REINFECTION: IMPORTANT CAUSE OF TB REOCCURRENCE?

In areas with a low incidence of tuberculosis (TB), conventional wisdom holds that disease recrudescence is more likely due to endogenous reactivation than to exogenous reinfection. However, results of a study suggest that even in areas with relatively low TB rates, exogenous reinfection may be an important cause of recurrence.

Caminero et al reviewed the records from 1991 through 1996 of 962 patients who had culture-confirmed tuberculosis. Of these, 23 (2.4%) had culture specimens that yielded Mycobacterium tuberculosis on two occasions at least 12 months apart. Eighteen of the 23 had bacterial DNA available for genotypic analysis.

In eight (44%) of the 18 patients, the genotype of the recurrent isolate had a pattern that was different from that of the initial isolate, suggesting exogenous reinfection. In the 10 remaining patients, the initial and final genotypes were identical, indicating endogenous reactivation. There was no difference in the median age of the two groups or in the median time to recurrence. Two patients with exogenous reinfection and three with endogenous reactivation were infected with the human immunodeficiency virus.

Caminero JA, Pena MJ, Campos-Herrero MI, et al. Exogenous reinfection with tuberculosis on a European island with a moderate incidence of disease. Am J Respir Crit Care Med. 2001;163:717-720.

FYI Study reveals health care disparity

A University of Michigan Health System study of outpatient claim forms from a single managed care organization indicates that asthmatic children who are insured by Medicaid are a third as likely to see a specialist for their condition than their privately insured counterparts. This disparity persisted even when patient age and asthma severity were factored out. Of 886 patients younger than 19 years, 30% were insured by Medicaid. While 21% of the 886 visited subspecialists, far fewer of the Medicaid-insured children were referred for specialist care. Asthmatic children who don’t see specialists may not be receiving the care that helps them avoid emergency department visits and hospitalization, the report said.

Source: Gavin K. Kids on Medicaid less likely to see specialist for asthma care, study finds. Available at: www.med.umich.edu/opm/newspage/cabana.htm. Accessed May 17, 2001.