Study Defines Scope of Vaccine-Preventable Infections in Asia

Two bacteria, Streptococcus pneumoniae and Haemophilus influenzae, are leading causes of meningitis and pneumonia worldwide, and yet both these health foes are easily prevented by available vaccines. These two common vaccines, however, often are not used in less developed countries because health care workers think the diseases they prevent are infrequent or unimportant. Now, a group of investigators from six INCLEN (International Clinical Epidemiology Network) academic hospitals in India, in collaboration with the Johns Hopkins School of Public Health, have conducted a prospective surveillance study to determine the most common serotypes of these two bacterial causes of meningitis and pneumonia, the characteristics of preventable invasive infections, and their patterns of antimicrobial susceptibility. The results of the four-year study were published in the April 10, 1999, issue of The Lancet.

The study's findings are crucial in formulating vaccines for Asian populations, and in describing antimicrobial resistance patterns. Since the routine use of conjugate vaccines against H. influenzae type-b (Hib) in the United States in 1988, for instance, cases of meningitis have decreased by more than 95 percent, and scientists now believe that adequate vaccine coverage will substantially reduce morbidity and mortality from vaccine-preventable infections (including pneumonia) in the developing world as well.

Mark Steinhoff, MD, professor, International Health, Pediatrics, and Epidemiology at Johns Hopkins School of Public Health, said, "The types of infections and levels of drug resistance we have found in India are similar to what have been found in Bangladesh and Pakistan, and may be indicative of patterns in other parts of Asia as well. The international community urgently needs to speed the introduction of vaccines and curb the consumption of antibiotic drugs."

In collaboration with the INCLEN researchers in India, Dr. Steinhoff and his colleagues studied 5,612 patients with suspected invasive infections at six hospitals in India from October 1993 to September 1997. The most commonly found pneumococcal serotypes were 1, 6, 19, 7, 5, 15, 14, 4, 16 and 18, with type-1 found in 25 percent of cases. Ninety-seven percent of the H. influenzae isolates cultured were type-b (vaccine preventable) and one each was identified as types-a, -d and -e.

The researchers found rates of antibiotic resistance as high as 85 percent for some strains of pneumococcus. Interestingly, drug resistance in S. pneumoniae was significantly higher in cities than in rural areas, and Dr. Steinhoff postulated that this was due to the higher availability of over-the-counter antibiotics in cities. Thus, in New Delhi and Vellore, respectively, S. pneumoniae resistance to cotrimoxazole was found in 78 and 39 percent of samples, and chloramphenicol resistance was found in 38 and 8 percent. The researchers also found that more than 60 percent of H. influenzae samples were intermediately or fully resistant to chloramphenicol, and that 46 to 55 percent were resistant to trimethoprim-sulfamethoxazole, ampicillin, or erythromycin. No isolates of either S. pneumoniae or H. influenzae were resistant to the third generation cephalosporin, cefotaxime.

The study included INCLEN investigators from the All India Institute of Medical Science in New Delhi; King George's Medical College in Lucknow; Government Medical College in Nagpur; Madras Medical College in Chennai; Trivandrum Medical College in Thiruvananthapuram; and the Christian Medical College in Vellore.

The study was supported by the United States Agency for International Development through the International Clinical Epidemiology Network (INCLEN) and Johns Hopkins Family Health and Child Survival.