Shigella sonnei infection is an inconvenient and possibly serious health threat to travelers, expatriates, and soldiers who enter less-developed countries. For example, S. sonnei was responsible for 54% of all Shigella infections in a survey of almost 2000 clinical isolates collected over a 13-year period from Finnish travelers (calculated from data in reference 9). Of travelers suffering from shigellosis while they were visiting Africa, 43% were infected with S. sonnei, and 51% of the travelers with shigellosis in the Far East were infected with this species. For Shigella-positive Finnish travelers in Europe, South and Central America, the Soviet Union, and the Middle East the percentages of infection with S. sonnei isolates were somewhat higher, ranging from 60% to 67%. These and other data suggest that a vaccine protecting against S. sonnei would eliminate a majority of the shigellosis cases experienced by travelers, expatriates, and soldiers. For example, such a vaccine would have protected troops from almost 90% of shigellosis during Operation Desert Shield (10).The predominance of S. sonnei as a cause of diarrhea in travelers is sometimes in stark contrast to the occurrence of this species among indigenous peoples. For example, S. sonnei was isolated from only 3% of native patients suffering from shigellosis in Sub-Saharan Africa, 5% of native patients in South Asia, and 15% of native patients in East Asia and the Pacific. This species did not predominate in native patients with shigellosis even in the Middle East (29% of isolates) or in Latin America (31% of isolates) (16). It is well known that the general level of environmental and personal hygiene affects the proportions of shigellosis that are attributable to S. sonnei and to Shigella flexneri. Improved hygiene reduces the ratio of S. flexneri (serogroup B) to S. sonnei (serogroup D) (B:D ratio) (2). Importantly, the B:D ratio can vary greatly within a relatively small geographical area. In southern Israel, for example, S. sonnei causes more than 70% of the shigellosis in the urban Jewish population of Beer-Sheva, while S. flexneri causes almost 70% of the shigellosis in the Muslim Bedouins living in the adjacent Negev desert towns and settlements (6). Since travelers from industrialized countries tend to lodge and dine in comparatively well-developed urban environments, they are exposed to S. sonnei more often than would be predicted from the overall B:D ratio for a less-developed country.
During an outbreak of severe pneumonia among new army recruits, an epidemiological investigation combined with repeated nasopharyngeal/oropharyngeal cultures from sick and healthy contacts subjects was conducted. Fifteen pneumonia cases and 19 influenza-like illness cases occurred among 596 recruits over a 4-week period in December 2005. Pneumonia attack rates reached up to 5.5%. A single pneumococcus serotype 5 clone was isolated from blood or sputum cultures in 4 patients and 30/124 (24.1%) contacts. Immunization with 23-valent polysaccharide vaccine supplemented with a 2-dose azithromycin mass treatment rapidly terminated the outbreak. Carriage rates dropped to <1%, 24 and 45 days after intervention.
An enzyme-linked immunosorbent assay system using oocyst lysate as antigen was used to detect serum- specific antibody responses to Cryptosporidium parvum between 1989 and 1994 in consecutive sera obtained at birth, and at the age of 6, 12, and 23 months, from 52 infants living in a Bedouin town located in the south of Israel. The serologic tests revealed high levels of immunoglobulin G anti-Cryptosporidium at birth that dropped significantly by the age of 6 months and then rose continuously to a geometric mean titer of 481 at age 23 months. The serum immunoglobulin M Cryptosporidium antibodies rose continuously from nearly undetectable levels at birth to a geometric mean titer of 471 (157-fold increase) at age 23 months. All the subjects already showed at 6 months a significant rise in immunoglobulin M. A significant rise in immunoglobulin A titers was detected in 48% and 91% of subjects at 6 and 23 months, respectively. By monthly surveillance, microscopy using the modified Ziehl-Neelsen method and confirmed by indirect immunofluorescence assay detected Cryptosporidium antigens in only 11% at age 6 months and 48% at age 23 months. The extent of exposure to Cryptosporidium immediately after birth as detected by serology is much higher than that predicted by frequent prospective assessment of stool samples.
Our study demonstrates the possible ramifications of the combination of a virulent and highly infective S. pyogenes strain and poor living conditions, and it emphasizes the importance of early intervention in such conditions.
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