To Örebro University

BACKGROUND: The use of nasopharyngeal secretions to enhance diagnostic yields of pneumococcal aetiology in community-acquired pneumonia (CAP) is of interest. We evaluated the Binax NOW Streptococcus pneumoniae immunochromatographic test (ICT) on nasopharyngeal aspirates (NPA) in order to support pneumococcal aetiology in CAP.

METHODS: The NPA ICT was applied on 180 adult CAP patients and 64 healthy controls. The rate of pneumococcal detection in the nasopharynx was compared to rates for lytA polymerase chain reaction (PCR) and culture on NPA.

RESULTS: According to blood and sputum culture and urine ICT, the test sensitivity in 59 patients with a pneumococcal aetiology was 81%. The specificity was suboptimal, with 72% negative tests among CAP patients without a pneumococcal aetiology. However, the test was positive in only 11% of patients with atypical pneumonia and in 4.7% of healthy controls. The positivity rate was higher for NPA ICT compared to culture on NPA in all CAP patients, and to both PCR and culture on NPA in non-pneumococcal non-atypical CAP patients. In 113 (63%) patients with β-lactam monotherapy, cure without treatment alteration was noted more often in cases with positive compared to negative NPA ICT at admission (91% vs 69%; p < 0.01).

CONCLUSIONS: The high sensitivity and the low positivity rates in patients with atypical pneumonia and healthy controls, in combination with the correlation between positive test results and clinical cure with β-lactam therapy, may support a pneumococcal aetiology in CAP in populations with low pneumococcal carriage rates.

We studied the immunoglobulin (Ig) response to causative serotype-specific capsular polysaccharides in adult pneumococcal pneumonia patients. The serotypes were grouped according to their degree of encapsulation and invasive potential. Seventy patients with pneumococcal pneumonia, 20 of whom were bacteremic, were prospectively studied. All pneumococcal isolates from the patients were serotyped, and the Ig titers to the homologous serotype were determined in acute- and convalescent-phase sera using a serotype-specific enzyme-linked immunosorbent assay. The Ig titers were lower in bacteremic cases than in nonbacteremic cases (P < 0.042). The Ig titer ratio (convalescent/acute titer) was ≥2 in 33 patients, 1 to 1.99 in 20 patients, and <1 in 17 patients. Patients ≥65 years old had a lower median Ig titer ratio than did younger patients (P < 0.031). The patients with serotypes with a thin capsule (1, 4, 7F, 9N, 9V, and 14) and medium/high invasive potential (1, 4, 7F, 9N, 9V, 14, and 18C) had higher Ig titer ratios than did patients with serotypes with a thick capsule (3, 6B, 11A, 18C, 19A, 19F, and 23F) and low invasive potential (3, 6B, 19A, 19F, and 23F) (P < 0.05 for both comparisons after adjustment for age). Ig titer ratios of <1 were predominantly noted in patients with serotypes with a thick capsule. In 8 patients with pneumococcal DNA detected in plasma, the three patients with the highest DNA load had the lowest Ig titer ratios. In conclusion, a high antibody response was associated with serotypes with a thin capsule and medium/high invasive potential, although a low antibody response was associated with serotypes with a thick capsule and a high pneumococcal plasma load.