Infectious disease considerations related to sudden flooding disasters for the emergency physician


  • Anthony Allworth, MB BS, FRACP, FRCPA, FACTM, Director.

Floods are one of a number of natural disasters that might occur without warning and that require knowledge of the array of infections that include the usual and less typically encountered organisms. The circumstances surrounding the event, the epidemiology of the event itself and its aftermath, and the nature of endemic pathogens all require special consideration by the astute emergency physician to tailor therapy to the event.

Emergency physicians are well aware that disasters largely comply to three phases.1 The Impact Phase (days 0–4) relates to the event itself with the resultant immediate consequences. The Post-impact Phase (4 days to 4 weeks) involves the sequence of events that occur subsequent to the inciting event that result in a series of pathologies as its consequence. The Recovery Phase (beyond 4 weeks) is largely positive, but might involve diseases that are either not normally seen or that are more common than usual.

In the Impact Phase, the focus is on the extraction of victims and management of resultant wounds. Depending on the circumstance the water might rise slowly (e.g. in riverine flooding downstream from a catchment) or violently (e.g. the Asian tsunami on Boxing Day 2004). In the context of violent surges often there are many wounds contaminated with mud and other polymicrobial substances (especially if the sewage system has been compromised). The principles learned from conflict wound management are applicable in this situation with thorough debridement and cleansing, avoidance of primary closure, and for major wounds or those involving tendons or joints appropriate antimicrobial prophylaxis that is confined to the period of the first 72 h or until wound closure (whichever is the shorter).

In the Post-impact Phase many infectious diseases might present a challenge to the response. Wound infections related to trauma during the Impact Phase might be due to the usual suspects such as Streptococcus pyogenes and Staphylococcus aureus, and clearly antimicrobial therapy requires coverage of these pathogens. Persons with comorbidities such as diabetes mellitus might be at increased risk of soft tissue infections, particularly those with peripheral neuropathy for instance involved in the Post-impact clean-up Phase and who suffer unrecognized injuries. Many of these wounds are exposed to contamination in water environments.

In fresh and brackish water Aeromonas sp. can play a role and require special consideration. Hence, for mild wound infections in this context, amoxycillin (to treat S. pyogenes) and cotrimoxazole (to treat S. aureus and Aeromonas sp.) are appropriate and generally well tolerated. For patients allergic to these agents or for more substantial infections, oral clindamycin and ciprofloxacin is a useful regimen, although gastrointestinal adverse events are more common with this combination. The Australian Government has recently added this indication for ciprofloxacin as a time-limited strategy to facilitate therapy in the current post-flooding environment. For those patients requiring inpatient care and i.v. therapy either i.v. ceftriaxone or ciprofloxacin together with i.v. lincomycin provides broad spectrum therapy including dealing with anaerobes.

In circumstances of exposure to seawater, such as might occur in the context of significant storm surges, Vibrio species including Vibrio vulnificus require consideration. Again ciprofloxacin might be used, or alternatively doxycycline might be combined with an agent such as clindamycin to cover the more typical pathogens. Clearly, tetanus immunization ± immunoglobulin is important in this circumstance, especially in parts of the world with low immunization rates overall – many cases of tetanus were seen after the Asian tsunami of 2004. In flooding events, animals as well as humans are displaced, resulting in the potential for increased numbers of bite wounds. These require pre-emptive therapy with amoxycillin-clavulanate, or alternatively doxycycline or cotrimoxazole together with metronidazole.2

A number of those caught up in floodwaters and their aftermath will present with a respiratory infection. The spectrum extends from near-drowning events to the more subacute presentation of a progressive multifocal pneumonic process such as that seen following the Asian tsunami of 2004.3 Again, the pathogens responsible will depend on local epidemiological factors. Tropical zones of Asia and areas of Queensland and the ‘Top End’ are endemic for melioidosis, an infection caused by Burkholderia pseudomallei that might present as an overwhelming multi-lobar pneumonia, a septicaemic illness, or as multifocal abscesses. Outside this geographical region, however, other gram-negative bacilli might also contribute to respiratory infections. These might occur as a consequence of direct aspiration of floodwaters, or as a result of inhalation of aerosolized material during the clean-up phase (as evidenced by the images of high-pressure hoses being used in confined spaces in many flood ravaged areas following the recent emergencies in Queensland and Victoria). These infections are often polymicrobial and might evolve into severe necrotizing pneumonias with abscesses and empyemas. As with wound infections, the ‘usual suspects’ will still be prevalent, with Streptococcus pneumoniae being common in these times. Hence, for typical presentations the usual antibiotic choices are appropriate (see the Australian Therapeutic Guidelines).2 However, a high level of suspicion for more unusual agents should be maintained, and therapy of atypical or severe pneumonias should include anti-Pseudomonal penicillins (e.g. piperacillin-tazobactam) or, when melioidosis is part of the differential, ceftazidime or meropenem, preferably with advice from an Infectious Diseases physician. Crowding that occurs in emergency shelters and displaced persons camps might result in the spread of viral respiratory pathogens including influenza, and in areas where it is prevalent tuberculosis, complicating this picture further. Finally, this setting of overcrowding when it occurs for extended periods in regions with low immunization rates might allow for outbreaks of measles or meningitis.

Gastrointestinal infections are always a consideration in the context of flood events. They are usually only an issue however, where sewage systems are compromised or when the availability of fresh water is restricted. Outbreaks of salmonellosis are not uncommon and difficulties maintaining food hygiene might contribute to these. In Haiti, 9 months after the earthquake in January, an unusual number of patients with acute watery diarrhoea and dehydration due to Vibrio cholera was noted. Within weeks there had been 16 111 persons hospitalized with acute watery diarrhoea with 992 cholera deaths. Although this infection is uncommon in most parts of the world, vigilance is clearly required. Norovirus and rotavirus might also be causes of diarrhoeal outbreaks, particularly in the setting of overcrowded emergency evacuation centres.4 Patients presenting with diarrhoeal illness should have stool cultures obtained. If fever and/or abdominal pain is present empiric therapy for bacterial enterocolitis should be commenced. Depending on knowledge of local antibiotic susceptibility patterns a quinolone (e.g. norfloxacin or ciprofloxacin) or azithromycin might be used.

A variety of other unusual infections might present in the Post-impact or Recovery Phases as non-specific febrile illnesses. Leptospirosis is caused by a spirochete that contaminates rodent urine and might become more prevalent in the aftermath of a flood as people conduct clean-ups and are exposed to a contaminated environment. Upon inoculation via abrasions or mucosal exposure, it presents following an incubation period of 5–14 days as a self-limited febrile illness commonly with headache, myalgia with muscle tenderness, conjunctival suffusion, and variable gastrointestinal and/or respiratory symptoms. It might progress to meningitis, hepatitis, renal impairment or multi-organ failure. Although the role for prophylaxis has not been clearly demonstrated,5 selected doxycycline prophylaxis for rescue workers might warrant consideration where leptospirosis has been demonstrated to be common.

Vector borne illnesses such as Dengue fever and malaria are frequently not prevalent during the Impact Phase as the vector habitat has been disturbed. However, their prevalence might rise over subsequent weeks as the breeding cycle is re-established and potentially amplified by the abundant standing water available.

Prevention is clearly important in all circumstances. Ensuring adequate preparation is part of life of many areas where extreme weather events regularly occur. However, when unusual flooding events occur the electronic media can be useful in providing positive messages, such as not wading in contaminated waters, utilizing appropriate footwear and protective garments including heavy duty gloves in the clean-up phase, and the use of masks/respirators in the context of potential aerosolization of floodwaters and detritus. This message is doubly important for persons who might be immunocompromised by illness (e.g. diabetic neuropathy) or therapies (e.g. corticosteroids).

Finally, although emergency physicians are all familiar with the need for personal protective equipment when called to attend pre-hospital scenarios, it is valuable to remind those attending flood incidents that sun protection, insect repellents and face masks with eye protection are still important, together with the more familiar protective clothing and gloves to avoid injury.

Competing interests

None declared.