Group A Beta-Hemolytic Streptococcal Pharyngitis Among U.S. Air Force Trainees -- Texas, 1988-89

In December 1988 and January 1989, an outbreak of pharyngitis caused by group A beta-hemolytic Streptococcus (GABHS) occurred among military trainees at Lackland Air Force Base, Texas. From January through November 1988, the incidence of culture-positive GABHS pharyngitis was 2.1 cases per 1000 trainees per month. By comparison, in December and January, the rates were 9.5 per 1000 and 18.7 per 1000, respectively. The outbreak prompted the administration of penicillin prophylaxis to all trainees ( greater than 6000)--the first time in at least 15 years that a mass prophylaxis program was implemented at this Air Force base.

Between December 23 and January 10, GABHS was isolated from throat swabs of 186 trainees from 13 flights (one flight=approximately 50 trainees) in four of eight squadrons (one squadron=16-20 flights). Each flight occupies a single open-bay sleeping area; each squadron occupies a single dormitory building. The outbreak was detected by a surveillance system for streptococcal pharyngitis: when streptococcal pharyngitis is detected in three or more trainees in a flight within a 7-day period, throat cultures are obtained from all members of that flight. If GABHS is isolated from greater than 10% of throat cultures, all persons in the flight who are not allergic to penicillin are given penicillin prophylaxis.

In the last week of December and first 2 weeks of January, 11 flights from three squadrons exceeded the threshold for prophylaxis. Six additional flights with less than three trainees with streptococcal pharyngitis were screened; two of those flights exceeded the threshold. Throat cultures were positive for 17% (17/101) of a sample of male trainees in the first half of their 4-week training course, compared with 31% (101/330) of a sample of trainees in the second half (relative risk=1.8; 95% confidence interval=1.1-2.9). All women were in the second half of their training.

In the second week of January, benzathine penicillin G (1.2 million units IM) was administered to greater than 6000 trainees already on the base. In addition, penicillin prophylaxis was initiated for all nonallergic, incoming personnel during their second week of training. During the third week of January, no flights exceeded the threshold. However, after two flights had three or more positive throat cultures in the fourth week of January, timing of prophylaxis was changed to the first week of training; subsequently, incidence rates of GABHS pharyngitis decreased markedly (Figure 1).

Routine prophylaxis was discontinued on April 30. In July, one flight exceeded the threshold for prophylaxis. No cases of acute rheumatic fever or other sequelae have been reported from Lackland Air Force Base or secondary training bases. Reported by: AH Mumm, COL, MC; CA Smith, LT COL, BSC, Epidemiology Div, US Air Force School of Aerospace Medicine, Human Systems Div, Brooks Air Force Base, CE Gookins, MAJ, BSC, Environmental Health Office, Wilford Hall US Air Force Medical Center, Lackland Air Force Base, Texas. Respiratory Diseases Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: During World Wars I and II, GABHS disease caused substantial morbidity among recruits (1), probably because of the introduction of large numbers of susceptible persons into crowded environments. A marked decrease in the incidence of GABHS disease and sequelae in military recruits occurred from 1965 to 1985 (1). This coincided with penicillin prophylaxis programs to prevent GABHS disease in military trainees and with a nationwide decrease in the incidence of rheumatic fever (2). By 1979, most military training centers had discontinued year-round prophylaxis of incoming recruits against GABHS disease (1).

This investigation and other recent reports demonstrate that military training centers remain at risk for outbreaks of GABHS-related disease and underscore the importance of surveillance in these settings (3,4). Although outbreaks of GABHS infections can be seasonal and self-limited, the abrupt decrease in incidence after January suggests that surveillance and antibiotic prophylaxis were important in limiting this outbreak. During other outbreaks of GABHS pharyngitis in military recruits, mass prophylaxis has been used successfully (5,6).

Some military training centers have policies for use of penicillin prophylaxis when the incidence of GABHS infections exceeds a specified threshold. The Armed Forces Epidemiological Board has suggested that when the incidence of GABHS disease exceeds 10 cases per 1000 trainees per week, epidemics of acute rheumatic fever may occur (7). The appropriateness of such policies for other institutional settings requires evaluation. State health departments are requested to notify CDC's Respiratory Diseases Branch, Division of Bacterial Diseases, Center for Infectious Diseases, at (404) 639-3021 about outbreaks of GABHS infections and/or their sequelae in such settings.

References

1. Thomas, RJ, Conwill DE, Morton DE, Brooks TJ, Holmes CK, Mahaffey WB. Penicillin prophylaxis for streptococcal infections in United States Navy and Marine Corps recruit camps, 1951-85. J Infect Dis 1988;10:125-30.

2. CDC. Acute rheumatic fever--Utah. MMWR 1987;36:108-10,115.

3. CDC. Acute rheumatic fever among Army trainees--Fort Leonard Wood, Missouri, 1987-1988. MMWR 1988;37:519-22.

4. Wallace MR, Garst PD, Papadimos TJ, Oldfield EC III. The return of acute rheumatic fever in young adults. JAMA 1989;262:2557-61.

5. Wannamaker LW, Denny FW, Perry WD, et al. The effect of penicillin prophylaxis on streptococcal disease rates and the carrier state. N Engl J Med 1953;249:1-7.

6. Davis J, Schmidt WD. Benzathine penicillin G: its effectiveness in the prevention of streptococcal infections in a heavily exposed population. N Engl J Med 1957;256:339-42.

7. Armed Forces Epidemiological Board. Recommendations of the Ad Hoc Committee on Prophylaxis of Streptococcal Infections of the Commission on Streptococcal Disease. Washington, DC: Armed Forces Epidemiological Board, 1959.

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